django/tests/cache/tests.py

# Unit tests for cache framework
# Uses whatever cache backend is set in the test settings file.
import copy
import io
import os
import pickle
import re
import shutil
import sys
import tempfile
import threading
import time
import unittest
import warnings
from pathlib import Path
from unittest import mock, skipIf

from django.conf import settings
from django.core import management, signals
from django.core.cache import (
    DEFAULT_CACHE_ALIAS, CacheHandler, CacheKeyWarning, InvalidCacheKey, cache,
    caches,
)
from django.core.cache.backends.base import InvalidCacheBackendError
from django.core.cache.utils import make_template_fragment_key
from django.db import close_old_connections, connection, connections
from django.http import (
    HttpRequest, HttpResponse, HttpResponseNotModified, StreamingHttpResponse,
)
from django.middleware.cache import (
    CacheMiddleware, FetchFromCacheMiddleware, UpdateCacheMiddleware,
)
from django.middleware.csrf import CsrfViewMiddleware
from django.template import engines
from django.template.context_processors import csrf
from django.template.response import TemplateResponse
from django.test import (
    RequestFactory, SimpleTestCase, TestCase, TransactionTestCase,
    ignore_warnings, override_settings,
)
from django.test.signals import setting_changed
from django.utils import timezone, translation
from django.utils.cache import (
    get_cache_key, learn_cache_key, patch_cache_control, patch_vary_headers,
)
from django.utils.deprecation import RemovedInDjango41Warning
from django.views.decorators.cache import cache_control, cache_page

from .models import Poll, expensive_calculation


# functions/classes for complex data type tests
def f():
    return 42


class C:
    def m(n):
        return 24


class Unpicklable:
    def __getstate__(self):
        raise pickle.PickleError()


def empty_response(request):
    return HttpResponse()


KEY_ERRORS_WITH_MEMCACHED_MSG = (
    'Cache key contains characters that will cause errors if used with '
    'memcached: %r'
)


@override_settings(CACHES={
    'default': {
        'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
    }
})
class DummyCacheTests(SimpleTestCase):
    # The Dummy cache backend doesn't really behave like a test backend,
    # so it has its own test case.

    def test_simple(self):
        "Dummy cache backend ignores cache set calls"
        cache.set("key", "value")
        self.assertIsNone(cache.get("key"))

    def test_add(self):
        "Add doesn't do anything in dummy cache backend"
        self.assertIs(cache.add("addkey1", "value"), True)
        self.assertIs(cache.add("addkey1", "newvalue"), True)
        self.assertIsNone(cache.get("addkey1"))

    def test_non_existent(self):
        "Nonexistent keys aren't found in the dummy cache backend"
        self.assertIsNone(cache.get("does_not_exist"))
        self.assertEqual(cache.get("does_not_exist", "bang!"), "bang!")

    def test_get_many(self):
        "get_many returns nothing for the dummy cache backend"
        cache.set_many({'a': 'a', 'b': 'b', 'c': 'c', 'd': 'd'})
        self.assertEqual(cache.get_many(['a', 'c', 'd']), {})
        self.assertEqual(cache.get_many(['a', 'b', 'e']), {})

    def test_get_many_invalid_key(self):
        msg = KEY_ERRORS_WITH_MEMCACHED_MSG % ':1:key with spaces'
        with self.assertWarnsMessage(CacheKeyWarning, msg):
            cache.get_many(['key with spaces'])

    def test_delete(self):
        "Cache deletion is transparently ignored on the dummy cache backend"
        cache.set_many({'key1': 'spam', 'key2': 'eggs'})
        self.assertIsNone(cache.get("key1"))
        self.assertIs(cache.delete("key1"), False)
        self.assertIsNone(cache.get("key1"))
        self.assertIsNone(cache.get("key2"))

    def test_has_key(self):
        "The has_key method doesn't ever return True for the dummy cache backend"
        cache.set("hello1", "goodbye1")
        self.assertIs(cache.has_key("hello1"), False)
        self.assertIs(cache.has_key("goodbye1"), False)

    def test_in(self):
        "The in operator doesn't ever return True for the dummy cache backend"
        cache.set("hello2", "goodbye2")
        self.assertNotIn("hello2", cache)
        self.assertNotIn("goodbye2", cache)

    def test_incr(self):
        "Dummy cache values can't be incremented"
        cache.set('answer', 42)
        with self.assertRaises(ValueError):
            cache.incr('answer')
        with self.assertRaises(ValueError):
            cache.incr('does_not_exist')

    def test_decr(self):
        "Dummy cache values can't be decremented"
        cache.set('answer', 42)
        with self.assertRaises(ValueError):
            cache.decr('answer')
        with self.assertRaises(ValueError):
            cache.decr('does_not_exist')

    def test_touch(self):
        """Dummy cache can't do touch()."""
        self.assertIs(cache.touch('whatever'), False)

    def test_data_types(self):
        "All data types are ignored equally by the dummy cache"
        stuff = {
            'string': 'this is a string',
            'int': 42,
            'list': [1, 2, 3, 4],
            'tuple': (1, 2, 3, 4),
            'dict': {'A': 1, 'B': 2},
            'function': f,
            'class': C,
        }
        cache.set("stuff", stuff)
        self.assertIsNone(cache.get("stuff"))

    def test_expiration(self):
        "Expiration has no effect on the dummy cache"
        cache.set('expire1', 'very quickly', 1)
        cache.set('expire2', 'very quickly', 1)
        cache.set('expire3', 'very quickly', 1)

        time.sleep(2)
        self.assertIsNone(cache.get("expire1"))

        self.assertIs(cache.add("expire2", "newvalue"), True)
        self.assertIsNone(cache.get("expire2"))
        self.assertIs(cache.has_key("expire3"), False)

    def test_unicode(self):
        "Unicode values are ignored by the dummy cache"
        stuff = {
            'ascii': 'ascii_value',
            'unicode_ascii': 'Iñtërnâtiônàlizætiøn1',
            'Iñtërnâtiônàlizætiøn': 'Iñtërnâtiônàlizætiøn2',
            'ascii2': {'x': 1}
        }
        for (key, value) in stuff.items():
            with self.subTest(key=key):
                cache.set(key, value)
                self.assertIsNone(cache.get(key))

    def test_set_many(self):
        "set_many does nothing for the dummy cache backend"
        self.assertEqual(cache.set_many({'a': 1, 'b': 2}), [])
        self.assertEqual(cache.set_many({'a': 1, 'b': 2}, timeout=2, version='1'), [])

    def test_set_many_invalid_key(self):
        msg = KEY_ERRORS_WITH_MEMCACHED_MSG % ':1:key with spaces'
        with self.assertWarnsMessage(CacheKeyWarning, msg):
            cache.set_many({'key with spaces': 'foo'})

    def test_delete_many(self):
        "delete_many does nothing for the dummy cache backend"
        cache.delete_many(['a', 'b'])

    def test_delete_many_invalid_key(self):
        msg = KEY_ERRORS_WITH_MEMCACHED_MSG % ':1:key with spaces'
        with self.assertWarnsMessage(CacheKeyWarning, msg):
            cache.delete_many({'key with spaces': 'foo'})

    def test_clear(self):
        "clear does nothing for the dummy cache backend"
        cache.clear()

    def test_incr_version(self):
        "Dummy cache versions can't be incremented"
        cache.set('answer', 42)
        with self.assertRaises(ValueError):
            cache.incr_version('answer')
        with self.assertRaises(ValueError):
            cache.incr_version('does_not_exist')

    def test_decr_version(self):
        "Dummy cache versions can't be decremented"
        cache.set('answer', 42)
        with self.assertRaises(ValueError):
            cache.decr_version('answer')
        with self.assertRaises(ValueError):
            cache.decr_version('does_not_exist')

    def test_get_or_set(self):
        self.assertEqual(cache.get_or_set('mykey', 'default'), 'default')
        self.assertIsNone(cache.get_or_set('mykey', None))

    def test_get_or_set_callable(self):
        def my_callable():
            return 'default'

        self.assertEqual(cache.get_or_set('mykey', my_callable), 'default')
        self.assertEqual(cache.get_or_set('mykey', my_callable()), 'default')


def custom_key_func(key, key_prefix, version):
    "A customized cache key function"
    return 'CUSTOM-' + '-'.join([key_prefix, str(version), key])


_caches_setting_base = {
    'default': {},
    'prefix': {'KEY_PREFIX': 'cacheprefix{}'.format(os.getpid())},
    'v2': {'VERSION': 2},
    'custom_key': {'KEY_FUNCTION': custom_key_func},
    'custom_key2': {'KEY_FUNCTION': 'cache.tests.custom_key_func'},
    'cull': {'OPTIONS': {'MAX_ENTRIES': 30}},
    'zero_cull': {'OPTIONS': {'CULL_FREQUENCY': 0, 'MAX_ENTRIES': 30}},
}


def caches_setting_for_tests(base=None, exclude=None, **params):
    # `base` is used to pull in the memcached config from the original settings,
    # `exclude` is a set of cache names denoting which `_caches_setting_base` keys
    # should be omitted.
    # `params` are test specific overrides and `_caches_settings_base` is the
    # base config for the tests.
    # This results in the following search order:
    # params -> _caches_setting_base -> base
    base = base or {}
    exclude = exclude or set()
    setting = {k: base.copy() for k in _caches_setting_base if k not in exclude}
    for key, cache_params in setting.items():
        cache_params.update(_caches_setting_base[key])
        cache_params.update(params)
    return setting


class BaseCacheTests:
    # A common set of tests to apply to all cache backends
    factory = RequestFactory()

    # RemovedInDjango41Warning: python-memcached doesn't support .get() with
    # default.
    supports_get_with_default = True

    # Some clients raise custom exceptions when .incr() or .decr() are called
    # with a non-integer value.
    incr_decr_type_error = TypeError

    def tearDown(self):
        cache.clear()

    def test_simple(self):
        # Simple cache set/get works
        cache.set("key", "value")
        self.assertEqual(cache.get("key"), "value")

    def test_default_used_when_none_is_set(self):
        """If None is cached, get() returns it instead of the default."""
        cache.set('key_default_none', None)
        self.assertIsNone(cache.get('key_default_none', default='default'))

    def test_add(self):
        # A key can be added to a cache
        self.assertIs(cache.add("addkey1", "value"), True)
        self.assertIs(cache.add("addkey1", "newvalue"), False)
        self.assertEqual(cache.get("addkey1"), "value")

    def test_prefix(self):
        # Test for same cache key conflicts between shared backend
        cache.set('somekey', 'value')

        # should not be set in the prefixed cache
        self.assertIs(caches['prefix'].has_key('somekey'), False)

        caches['prefix'].set('somekey', 'value2')

        self.assertEqual(cache.get('somekey'), 'value')
        self.assertEqual(caches['prefix'].get('somekey'), 'value2')

    def test_non_existent(self):
        """Nonexistent cache keys return as None/default."""
        self.assertIsNone(cache.get("does_not_exist"))
        self.assertEqual(cache.get("does_not_exist", "bang!"), "bang!")

    def test_get_many(self):
        # Multiple cache keys can be returned using get_many
        cache.set_many({'a': 'a', 'b': 'b', 'c': 'c', 'd': 'd'})
        self.assertEqual(cache.get_many(['a', 'c', 'd']), {'a': 'a', 'c': 'c', 'd': 'd'})
        self.assertEqual(cache.get_many(['a', 'b', 'e']), {'a': 'a', 'b': 'b'})
        self.assertEqual(cache.get_many(iter(['a', 'b', 'e'])), {'a': 'a', 'b': 'b'})
        cache.set_many({'x': None, 'y': 1})
        self.assertEqual(cache.get_many(['x', 'y']), {'x': None, 'y': 1})

    def test_delete(self):
        # Cache keys can be deleted
        cache.set_many({'key1': 'spam', 'key2': 'eggs'})
        self.assertEqual(cache.get("key1"), "spam")
        self.assertIs(cache.delete("key1"), True)
        self.assertIsNone(cache.get("key1"))
        self.assertEqual(cache.get("key2"), "eggs")

    def test_delete_nonexistent(self):
        self.assertIs(cache.delete('nonexistent_key'), False)

    def test_has_key(self):
        # The cache can be inspected for cache keys
        cache.set("hello1", "goodbye1")
        self.assertIs(cache.has_key("hello1"), True)
        self.assertIs(cache.has_key("goodbye1"), False)
        cache.set("no_expiry", "here", None)
        self.assertIs(cache.has_key("no_expiry"), True)
        cache.set('null', None)
        self.assertIs(
            cache.has_key('null'),
            True if self.supports_get_with_default else False,
        )

    def test_in(self):
        # The in operator can be used to inspect cache contents
        cache.set("hello2", "goodbye2")
        self.assertIn("hello2", cache)
        self.assertNotIn("goodbye2", cache)
        cache.set('null', None)
        if self.supports_get_with_default:
            self.assertIn('null', cache)
        else:
            self.assertNotIn('null', cache)

    def test_incr(self):
        # Cache values can be incremented
        cache.set('answer', 41)
        self.assertEqual(cache.incr('answer'), 42)
        self.assertEqual(cache.get('answer'), 42)
        self.assertEqual(cache.incr('answer', 10), 52)
        self.assertEqual(cache.get('answer'), 52)
        self.assertEqual(cache.incr('answer', -10), 42)
        with self.assertRaises(ValueError):
            cache.incr('does_not_exist')
        cache.set('null', None)
        with self.assertRaises(self.incr_decr_type_error):
            cache.incr('null')

    def test_decr(self):
        # Cache values can be decremented
        cache.set('answer', 43)
        self.assertEqual(cache.decr('answer'), 42)
        self.assertEqual(cache.get('answer'), 42)
        self.assertEqual(cache.decr('answer', 10), 32)
        self.assertEqual(cache.get('answer'), 32)
        self.assertEqual(cache.decr('answer', -10), 42)
        with self.assertRaises(ValueError):
            cache.decr('does_not_exist')
        cache.set('null', None)
        with self.assertRaises(self.incr_decr_type_error):
            cache.decr('null')

    def test_close(self):
        self.assertTrue(hasattr(cache, 'close'))
        cache.close()

    def test_data_types(self):
        # Many different data types can be cached
        stuff = {
            'string': 'this is a string',
            'int': 42,
            'list': [1, 2, 3, 4],
            'tuple': (1, 2, 3, 4),
            'dict': {'A': 1, 'B': 2},
            'function': f,
            'class': C,
        }
        cache.set("stuff", stuff)
        self.assertEqual(cache.get("stuff"), stuff)

    def test_cache_read_for_model_instance(self):
        # Don't want fields with callable as default to be called on cache read
        expensive_calculation.num_runs = 0
        Poll.objects.all().delete()
        my_poll = Poll.objects.create(question="Well?")
        self.assertEqual(Poll.objects.count(), 1)
        pub_date = my_poll.pub_date
        cache.set('question', my_poll)
        cached_poll = cache.get('question')
        self.assertEqual(cached_poll.pub_date, pub_date)
        # We only want the default expensive calculation run once
        self.assertEqual(expensive_calculation.num_runs, 1)

    def test_cache_write_for_model_instance_with_deferred(self):
        # Don't want fields with callable as default to be called on cache write
        expensive_calculation.num_runs = 0
        Poll.objects.all().delete()
        Poll.objects.create(question="What?")
        self.assertEqual(expensive_calculation.num_runs, 1)
        defer_qs = Poll.objects.all().defer('question')
        self.assertEqual(defer_qs.count(), 1)
        self.assertEqual(expensive_calculation.num_runs, 1)
        cache.set('deferred_queryset', defer_qs)
        # cache set should not re-evaluate default functions
        self.assertEqual(expensive_calculation.num_runs, 1)

    def test_cache_read_for_model_instance_with_deferred(self):
        # Don't want fields with callable as default to be called on cache read
        expensive_calculation.num_runs = 0
        Poll.objects.all().delete()
        Poll.objects.create(question="What?")
        self.assertEqual(expensive_calculation.num_runs, 1)
        defer_qs = Poll.objects.all().defer('question')
        self.assertEqual(defer_qs.count(), 1)
        cache.set('deferred_queryset', defer_qs)
        self.assertEqual(expensive_calculation.num_runs, 1)
        runs_before_cache_read = expensive_calculation.num_runs
        cache.get('deferred_queryset')
        # We only want the default expensive calculation run on creation and set
        self.assertEqual(expensive_calculation.num_runs, runs_before_cache_read)

    def test_expiration(self):
        # Cache values can be set to expire
        cache.set('expire1', 'very quickly', 1)
        cache.set('expire2', 'very quickly', 1)
        cache.set('expire3', 'very quickly', 1)

        time.sleep(2)
        self.assertIsNone(cache.get("expire1"))

        self.assertIs(cache.add("expire2", "newvalue"), True)
        self.assertEqual(cache.get("expire2"), "newvalue")
        self.assertIs(cache.has_key("expire3"), False)

    def test_touch(self):
        # cache.touch() updates the timeout.
        cache.set('expire1', 'very quickly', timeout=1)
        self.assertIs(cache.touch('expire1', timeout=4), True)
        time.sleep(2)
        self.assertIs(cache.has_key('expire1'), True)
        time.sleep(3)
        self.assertIs(cache.has_key('expire1'), False)
        # cache.touch() works without the timeout argument.
        cache.set('expire1', 'very quickly', timeout=1)
        self.assertIs(cache.touch('expire1'), True)
        time.sleep(2)
        self.assertIs(cache.has_key('expire1'), True)

        self.assertIs(cache.touch('nonexistent'), False)

    def test_unicode(self):
        # Unicode values can be cached
        stuff = {
            'ascii': 'ascii_value',
            'unicode_ascii': 'Iñtërnâtiônàlizætiøn1',
            'Iñtërnâtiônàlizætiøn': 'Iñtërnâtiônàlizætiøn2',
            'ascii2': {'x': 1}
        }
        # Test `set`
        for (key, value) in stuff.items():
            with self.subTest(key=key):
                cache.set(key, value)
                self.assertEqual(cache.get(key), value)

        # Test `add`
        for (key, value) in stuff.items():
            with self.subTest(key=key):
                self.assertIs(cache.delete(key), True)
                self.assertIs(cache.add(key, value), True)
                self.assertEqual(cache.get(key), value)

        # Test `set_many`
        for (key, value) in stuff.items():
            self.assertIs(cache.delete(key), True)
        cache.set_many(stuff)
        for (key, value) in stuff.items():
            with self.subTest(key=key):
                self.assertEqual(cache.get(key), value)

    def test_binary_string(self):
        # Binary strings should be cacheable
        from zlib import compress, decompress
        value = 'value_to_be_compressed'
        compressed_value = compress(value.encode())

        # Test set
        cache.set('binary1', compressed_value)
        compressed_result = cache.get('binary1')
        self.assertEqual(compressed_value, compressed_result)
        self.assertEqual(value, decompress(compressed_result).decode())

        # Test add
        self.assertIs(cache.add('binary1-add', compressed_value), True)
        compressed_result = cache.get('binary1-add')
        self.assertEqual(compressed_value, compressed_result)
        self.assertEqual(value, decompress(compressed_result).decode())

        # Test set_many
        cache.set_many({'binary1-set_many': compressed_value})
        compressed_result = cache.get('binary1-set_many')
        self.assertEqual(compressed_value, compressed_result)
        self.assertEqual(value, decompress(compressed_result).decode())

    def test_set_many(self):
        # Multiple keys can be set using set_many
        cache.set_many({"key1": "spam", "key2": "eggs"})
        self.assertEqual(cache.get("key1"), "spam")
        self.assertEqual(cache.get("key2"), "eggs")

    def test_set_many_returns_empty_list_on_success(self):
        """set_many() returns an empty list when all keys are inserted."""
        failing_keys = cache.set_many({'key1': 'spam', 'key2': 'eggs'})
        self.assertEqual(failing_keys, [])

    def test_set_many_expiration(self):
        # set_many takes a second ``timeout`` parameter
        cache.set_many({"key1": "spam", "key2": "eggs"}, 1)
        time.sleep(2)
        self.assertIsNone(cache.get("key1"))
        self.assertIsNone(cache.get("key2"))

    def test_delete_many(self):
        # Multiple keys can be deleted using delete_many
        cache.set_many({'key1': 'spam', 'key2': 'eggs', 'key3': 'ham'})
        cache.delete_many(["key1", "key2"])
        self.assertIsNone(cache.get("key1"))
        self.assertIsNone(cache.get("key2"))
        self.assertEqual(cache.get("key3"), "ham")

    def test_clear(self):
        # The cache can be emptied using clear
        cache.set_many({'key1': 'spam', 'key2': 'eggs'})
        cache.clear()
        self.assertIsNone(cache.get("key1"))
        self.assertIsNone(cache.get("key2"))

    def test_long_timeout(self):
        """
        Follow memcached's convention where a timeout greater than 30 days is
        treated as an absolute expiration timestamp instead of a relative
        offset (#12399).
        """
        cache.set('key1', 'eggs', 60 * 60 * 24 * 30 + 1)  # 30 days + 1 second
        self.assertEqual(cache.get('key1'), 'eggs')

        self.assertIs(cache.add('key2', 'ham', 60 * 60 * 24 * 30 + 1), True)
        self.assertEqual(cache.get('key2'), 'ham')

        cache.set_many({'key3': 'sausage', 'key4': 'lobster bisque'}, 60 * 60 * 24 * 30 + 1)
        self.assertEqual(cache.get('key3'), 'sausage')
        self.assertEqual(cache.get('key4'), 'lobster bisque')

    def test_forever_timeout(self):
        """
        Passing in None into timeout results in a value that is cached forever
        """
        cache.set('key1', 'eggs', None)
        self.assertEqual(cache.get('key1'), 'eggs')

        self.assertIs(cache.add('key2', 'ham', None), True)
        self.assertEqual(cache.get('key2'), 'ham')
        self.assertIs(cache.add('key1', 'new eggs', None), False)
        self.assertEqual(cache.get('key1'), 'eggs')

        cache.set_many({'key3': 'sausage', 'key4': 'lobster bisque'}, None)
        self.assertEqual(cache.get('key3'), 'sausage')
        self.assertEqual(cache.get('key4'), 'lobster bisque')

        cache.set('key5', 'belgian fries', timeout=1)
        self.assertIs(cache.touch('key5', timeout=None), True)
        time.sleep(2)
        self.assertEqual(cache.get('key5'), 'belgian fries')

    def test_zero_timeout(self):
        """
        Passing in zero into timeout results in a value that is not cached
        """
        cache.set('key1', 'eggs', 0)
        self.assertIsNone(cache.get('key1'))

        self.assertIs(cache.add('key2', 'ham', 0), True)
        self.assertIsNone(cache.get('key2'))

        cache.set_many({'key3': 'sausage', 'key4': 'lobster bisque'}, 0)
        self.assertIsNone(cache.get('key3'))
        self.assertIsNone(cache.get('key4'))

        cache.set('key5', 'belgian fries', timeout=5)
        self.assertIs(cache.touch('key5', timeout=0), True)
        self.assertIsNone(cache.get('key5'))

    def test_float_timeout(self):
        # Make sure a timeout given as a float doesn't crash anything.
        cache.set("key1", "spam", 100.2)
        self.assertEqual(cache.get("key1"), "spam")

    def _perform_cull_test(self, cull_cache_name, initial_count, final_count):
        try:
            cull_cache = caches[cull_cache_name]
        except InvalidCacheBackendError:
            self.skipTest("Culling isn't implemented.")

        # Create initial cache key entries. This will overflow the cache,
        # causing a cull.
        for i in range(1, initial_count):
            cull_cache.set('cull%d' % i, 'value', 1000)
        count = 0
        # Count how many keys are left in the cache.
        for i in range(1, initial_count):
            if cull_cache.has_key('cull%d' % i):
                count += 1
        self.assertEqual(count, final_count)

    def test_cull(self):
        self._perform_cull_test('cull', 50, 29)

    def test_zero_cull(self):
        self._perform_cull_test('zero_cull', 50, 19)

    def test_cull_delete_when_store_empty(self):
        try:
            cull_cache = caches['cull']
        except InvalidCacheBackendError:
            self.skipTest("Culling isn't implemented.")
        old_max_entries = cull_cache._max_entries
        # Force _cull to delete on first cached record.
        cull_cache._max_entries = -1
        try:
            cull_cache.set('force_cull_delete', 'value', 1000)
            self.assertIs(cull_cache.has_key('force_cull_delete'), True)
        finally:
            cull_cache._max_entries = old_max_entries

    def _perform_invalid_key_test(self, key, expected_warning):
        """
        All the builtin backends should warn (except memcached that should
        error) on keys that would be refused by memcached. This encourages
        portable caching code without making it too difficult to use production
        backends with more liberal key rules. Refs #6447.
        """
        # mimic custom ``make_key`` method being defined since the default will
        # never show the below warnings
        def func(key, *args):
            return key

        old_func = cache.key_func
        cache.key_func = func

        tests = [
            ('add', [key, 1]),
            ('get', [key]),
            ('set', [key, 1]),
            ('incr', [key]),
            ('decr', [key]),
            ('touch', [key]),
            ('delete', [key]),
            ('get_many', [[key, 'b']]),
            ('set_many', [{key: 1, 'b': 2}]),
            ('delete_many', [{key: 1, 'b': 2}]),
        ]
        try:
            for operation, args in tests:
                with self.subTest(operation=operation):
                    with self.assertWarns(CacheKeyWarning) as cm:
                        getattr(cache, operation)(*args)
                    self.assertEqual(str(cm.warning), expected_warning)
        finally:
            cache.key_func = old_func

    def test_invalid_key_characters(self):
        # memcached doesn't allow whitespace or control characters in keys.
        key = 'key with spaces and 清'
        self._perform_invalid_key_test(key, KEY_ERRORS_WITH_MEMCACHED_MSG % key)

    def test_invalid_key_length(self):
        # memcached limits key length to 250.
        key = ('a' * 250) + '清'
        expected_warning = (
            'Cache key will cause errors if used with memcached: '
            '%r (longer than %s)' % (key, 250)
        )
        self._perform_invalid_key_test(key, expected_warning)

    def test_cache_versioning_get_set(self):
        # set, using default version = 1
        cache.set('answer1', 42)
        self.assertEqual(cache.get('answer1'), 42)
        self.assertEqual(cache.get('answer1', version=1), 42)
        self.assertIsNone(cache.get('answer1', version=2))

        self.assertIsNone(caches['v2'].get('answer1'))
        self.assertEqual(caches['v2'].get('answer1', version=1), 42)
        self.assertIsNone(caches['v2'].get('answer1', version=2))

        # set, default version = 1, but manually override version = 2
        cache.set('answer2', 42, version=2)
        self.assertIsNone(cache.get('answer2'))
        self.assertIsNone(cache.get('answer2', version=1))
        self.assertEqual(cache.get('answer2', version=2), 42)

        self.assertEqual(caches['v2'].get('answer2'), 42)
        self.assertIsNone(caches['v2'].get('answer2', version=1))
        self.assertEqual(caches['v2'].get('answer2', version=2), 42)

        # v2 set, using default version = 2
        caches['v2'].set('answer3', 42)
        self.assertIsNone(cache.get('answer3'))
        self.assertIsNone(cache.get('answer3', version=1))
        self.assertEqual(cache.get('answer3', version=2), 42)

        self.assertEqual(caches['v2'].get('answer3'), 42)
        self.assertIsNone(caches['v2'].get('answer3', version=1))
        self.assertEqual(caches['v2'].get('answer3', version=2), 42)

        # v2 set, default version = 2, but manually override version = 1
        caches['v2'].set('answer4', 42, version=1)
        self.assertEqual(cache.get('answer4'), 42)
        self.assertEqual(cache.get('answer4', version=1), 42)
        self.assertIsNone(cache.get('answer4', version=2))

        self.assertIsNone(caches['v2'].get('answer4'))
        self.assertEqual(caches['v2'].get('answer4', version=1), 42)
        self.assertIsNone(caches['v2'].get('answer4', version=2))

    def test_cache_versioning_add(self):

        # add, default version = 1, but manually override version = 2
        self.assertIs(cache.add('answer1', 42, version=2), True)
        self.assertIsNone(cache.get('answer1', version=1))
        self.assertEqual(cache.get('answer1', version=2), 42)

        self.assertIs(cache.add('answer1', 37, version=2), False)
        self.assertIsNone(cache.get('answer1', version=1))
        self.assertEqual(cache.get('answer1', version=2), 42)

        self.assertIs(cache.add('answer1', 37, version=1), True)
        self.assertEqual(cache.get('answer1', version=1), 37)
        self.assertEqual(cache.get('answer1', version=2), 42)

        # v2 add, using default version = 2
        self.assertIs(caches['v2'].add('answer2', 42), True)
        self.assertIsNone(cache.get('answer2', version=1))
        self.assertEqual(cache.get('answer2', version=2), 42)

        self.assertIs(caches['v2'].add('answer2', 37), False)
        self.assertIsNone(cache.get('answer2', version=1))
        self.assertEqual(cache.get('answer2', version=2), 42)

        self.assertIs(caches['v2'].add('answer2', 37, version=1), True)
        self.assertEqual(cache.get('answer2', version=1), 37)
        self.assertEqual(cache.get('answer2', version=2), 42)

        # v2 add, default version = 2, but manually override version = 1
        self.assertIs(caches['v2'].add('answer3', 42, version=1), True)
        self.assertEqual(cache.get('answer3', version=1), 42)
        self.assertIsNone(cache.get('answer3', version=2))

        self.assertIs(caches['v2'].add('answer3', 37, version=1), False)
        self.assertEqual(cache.get('answer3', version=1), 42)
        self.assertIsNone(cache.get('answer3', version=2))

        self.assertIs(caches['v2'].add('answer3', 37), True)
        self.assertEqual(cache.get('answer3', version=1), 42)
        self.assertEqual(cache.get('answer3', version=2), 37)

    def test_cache_versioning_has_key(self):
        cache.set('answer1', 42)

        # has_key
        self.assertIs(cache.has_key('answer1'), True)
        self.assertIs(cache.has_key('answer1', version=1), True)
        self.assertIs(cache.has_key('answer1', version=2), False)

        self.assertIs(caches['v2'].has_key('answer1'), False)
        self.assertIs(caches['v2'].has_key('answer1', version=1), True)
        self.assertIs(caches['v2'].has_key('answer1', version=2), False)

    def test_cache_versioning_delete(self):
        cache.set('answer1', 37, version=1)
        cache.set('answer1', 42, version=2)
        self.assertIs(cache.delete('answer1'), True)
        self.assertIsNone(cache.get('answer1', version=1))
        self.assertEqual(cache.get('answer1', version=2), 42)

        cache.set('answer2', 37, version=1)
        cache.set('answer2', 42, version=2)
        self.assertIs(cache.delete('answer2', version=2), True)
        self.assertEqual(cache.get('answer2', version=1), 37)
        self.assertIsNone(cache.get('answer2', version=2))

        cache.set('answer3', 37, version=1)
        cache.set('answer3', 42, version=2)
        self.assertIs(caches['v2'].delete('answer3'), True)
        self.assertEqual(cache.get('answer3', version=1), 37)
        self.assertIsNone(cache.get('answer3', version=2))

        cache.set('answer4', 37, version=1)
        cache.set('answer4', 42, version=2)
        self.assertIs(caches['v2'].delete('answer4', version=1), True)
        self.assertIsNone(cache.get('answer4', version=1))
        self.assertEqual(cache.get('answer4', version=2), 42)

    def test_cache_versioning_incr_decr(self):
        cache.set('answer1', 37, version=1)
        cache.set('answer1', 42, version=2)
        self.assertEqual(cache.incr('answer1'), 38)
        self.assertEqual(cache.get('answer1', version=1), 38)
        self.assertEqual(cache.get('answer1', version=2), 42)
        self.assertEqual(cache.decr('answer1'), 37)
        self.assertEqual(cache.get('answer1', version=1), 37)
        self.assertEqual(cache.get('answer1', version=2), 42)

        cache.set('answer2', 37, version=1)
        cache.set('answer2', 42, version=2)
        self.assertEqual(cache.incr('answer2', version=2), 43)
        self.assertEqual(cache.get('answer2', version=1), 37)
        self.assertEqual(cache.get('answer2', version=2), 43)
        self.assertEqual(cache.decr('answer2', version=2), 42)
        self.assertEqual(cache.get('answer2', version=1), 37)
        self.assertEqual(cache.get('answer2', version=2), 42)

        cache.set('answer3', 37, version=1)
        cache.set('answer3', 42, version=2)
        self.assertEqual(caches['v2'].incr('answer3'), 43)
        self.assertEqual(cache.get('answer3', version=1), 37)
        self.assertEqual(cache.get('answer3', version=2), 43)
        self.assertEqual(caches['v2'].decr('answer3'), 42)
        self.assertEqual(cache.get('answer3', version=1), 37)
        self.assertEqual(cache.get('answer3', version=2), 42)

        cache.set('answer4', 37, version=1)
        cache.set('answer4', 42, version=2)
        self.assertEqual(caches['v2'].incr('answer4', version=1), 38)
        self.assertEqual(cache.get('answer4', version=1), 38)
        self.assertEqual(cache.get('answer4', version=2), 42)
        self.assertEqual(caches['v2'].decr('answer4', version=1), 37)
        self.assertEqual(cache.get('answer4', version=1), 37)
        self.assertEqual(cache.get('answer4', version=2), 42)

    def test_cache_versioning_get_set_many(self):
        # set, using default version = 1
        cache.set_many({'ford1': 37, 'arthur1': 42})
        self.assertEqual(cache.get_many(['ford1', 'arthur1']), {'ford1': 37, 'arthur1': 42})
        self.assertEqual(cache.get_many(['ford1', 'arthur1'], version=1), {'ford1': 37, 'arthur1': 42})
        self.assertEqual(cache.get_many(['ford1', 'arthur1'], version=2), {})

        self.assertEqual(caches['v2'].get_many(['ford1', 'arthur1']), {})
        self.assertEqual(caches['v2'].get_many(['ford1', 'arthur1'], version=1), {'ford1': 37, 'arthur1': 42})
        self.assertEqual(caches['v2'].get_many(['ford1', 'arthur1'], version=2), {})

        # set, default version = 1, but manually override version = 2
        cache.set_many({'ford2': 37, 'arthur2': 42}, version=2)
        self.assertEqual(cache.get_many(['ford2', 'arthur2']), {})
        self.assertEqual(cache.get_many(['ford2', 'arthur2'], version=1), {})
        self.assertEqual(cache.get_many(['ford2', 'arthur2'], version=2), {'ford2': 37, 'arthur2': 42})

        self.assertEqual(caches['v2'].get_many(['ford2', 'arthur2']), {'ford2': 37, 'arthur2': 42})
        self.assertEqual(caches['v2'].get_many(['ford2', 'arthur2'], version=1), {})
        self.assertEqual(caches['v2'].get_many(['ford2', 'arthur2'], version=2), {'ford2': 37, 'arthur2': 42})

        # v2 set, using default version = 2
        caches['v2'].set_many({'ford3': 37, 'arthur3': 42})
        self.assertEqual(cache.get_many(['ford3', 'arthur3']), {})
        self.assertEqual(cache.get_many(['ford3', 'arthur3'], version=1), {})
        self.assertEqual(cache.get_many(['ford3', 'arthur3'], version=2), {'ford3': 37, 'arthur3': 42})

        self.assertEqual(caches['v2'].get_many(['ford3', 'arthur3']), {'ford3': 37, 'arthur3': 42})
        self.assertEqual(caches['v2'].get_many(['ford3', 'arthur3'], version=1), {})
        self.assertEqual(caches['v2'].get_many(['ford3', 'arthur3'], version=2), {'ford3': 37, 'arthur3': 42})

        # v2 set, default version = 2, but manually override version = 1
        caches['v2'].set_many({'ford4': 37, 'arthur4': 42}, version=1)
        self.assertEqual(cache.get_many(['ford4', 'arthur4']), {'ford4': 37, 'arthur4': 42})
        self.assertEqual(cache.get_many(['ford4', 'arthur4'], version=1), {'ford4': 37, 'arthur4': 42})
        self.assertEqual(cache.get_many(['ford4', 'arthur4'], version=2), {})

        self.assertEqual(caches['v2'].get_many(['ford4', 'arthur4']), {})
        self.assertEqual(caches['v2'].get_many(['ford4', 'arthur4'], version=1), {'ford4': 37, 'arthur4': 42})
        self.assertEqual(caches['v2'].get_many(['ford4', 'arthur4'], version=2), {})

    def test_incr_version(self):
        cache.set('answer', 42, version=2)
        self.assertIsNone(cache.get('answer'))
        self.assertIsNone(cache.get('answer', version=1))
        self.assertEqual(cache.get('answer', version=2), 42)
        self.assertIsNone(cache.get('answer', version=3))

        self.assertEqual(cache.incr_version('answer', version=2), 3)
        self.assertIsNone(cache.get('answer'))
        self.assertIsNone(cache.get('answer', version=1))
        self.assertIsNone(cache.get('answer', version=2))
        self.assertEqual(cache.get('answer', version=3), 42)

        caches['v2'].set('answer2', 42)
        self.assertEqual(caches['v2'].get('answer2'), 42)
        self.assertIsNone(caches['v2'].get('answer2', version=1))
        self.assertEqual(caches['v2'].get('answer2', version=2), 42)
        self.assertIsNone(caches['v2'].get('answer2', version=3))

        self.assertEqual(caches['v2'].incr_version('answer2'), 3)
        self.assertIsNone(caches['v2'].get('answer2'))
        self.assertIsNone(caches['v2'].get('answer2', version=1))
        self.assertIsNone(caches['v2'].get('answer2', version=2))
        self.assertEqual(caches['v2'].get('answer2', version=3), 42)

        with self.assertRaises(ValueError):
            cache.incr_version('does_not_exist')

        cache.set('null', None)
        if self.supports_get_with_default:
            self.assertEqual(cache.incr_version('null'), 2)
        else:
            with self.assertRaises(self.incr_decr_type_error):
                cache.incr_version('null')

    def test_decr_version(self):
        cache.set('answer', 42, version=2)
        self.assertIsNone(cache.get('answer'))
        self.assertIsNone(cache.get('answer', version=1))
        self.assertEqual(cache.get('answer', version=2), 42)

        self.assertEqual(cache.decr_version('answer', version=2), 1)
        self.assertEqual(cache.get('answer'), 42)
        self.assertEqual(cache.get('answer', version=1), 42)
        self.assertIsNone(cache.get('answer', version=2))

        caches['v2'].set('answer2', 42)
        self.assertEqual(caches['v2'].get('answer2'), 42)
        self.assertIsNone(caches['v2'].get('answer2', version=1))
        self.assertEqual(caches['v2'].get('answer2', version=2), 42)

        self.assertEqual(caches['v2'].decr_version('answer2'), 1)
        self.assertIsNone(caches['v2'].get('answer2'))
        self.assertEqual(caches['v2'].get('answer2', version=1), 42)
        self.assertIsNone(caches['v2'].get('answer2', version=2))

        with self.assertRaises(ValueError):
            cache.decr_version('does_not_exist', version=2)

        cache.set('null', None, version=2)
        if self.supports_get_with_default:
            self.assertEqual(cache.decr_version('null', version=2), 1)
        else:
            with self.assertRaises(self.incr_decr_type_error):
                cache.decr_version('null', version=2)

    def test_custom_key_func(self):
        # Two caches with different key functions aren't visible to each other
        cache.set('answer1', 42)
        self.assertEqual(cache.get('answer1'), 42)
        self.assertIsNone(caches['custom_key'].get('answer1'))
        self.assertIsNone(caches['custom_key2'].get('answer1'))

        caches['custom_key'].set('answer2', 42)
        self.assertIsNone(cache.get('answer2'))
        self.assertEqual(caches['custom_key'].get('answer2'), 42)
        self.assertEqual(caches['custom_key2'].get('answer2'), 42)

    def test_cache_write_unpicklable_object(self):
        fetch_middleware = FetchFromCacheMiddleware(empty_response)
        fetch_middleware.cache = cache

        request = self.factory.get('/cache/test')
        request._cache_update_cache = True
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNone(get_cache_data)

        content = 'Testing cookie serialization.'

        def get_response(req):
            response = HttpResponse(content)
            response.set_cookie('foo', 'bar')
            return response

        update_middleware = UpdateCacheMiddleware(get_response)
        update_middleware.cache = cache
        response = update_middleware(request)

        get_cache_data = fetch_middleware.process_request(request)
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(get_cache_data.content, content.encode())
        self.assertEqual(get_cache_data.cookies, response.cookies)

        UpdateCacheMiddleware(lambda req: get_cache_data)(request)
        get_cache_data = fetch_middleware.process_request(request)
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(get_cache_data.content, content.encode())
        self.assertEqual(get_cache_data.cookies, response.cookies)

    def test_add_fail_on_pickleerror(self):
        # Shouldn't fail silently if trying to cache an unpicklable type.
        with self.assertRaises(pickle.PickleError):
            cache.add('unpicklable', Unpicklable())

    def test_set_fail_on_pickleerror(self):
        with self.assertRaises(pickle.PickleError):
            cache.set('unpicklable', Unpicklable())

    def test_get_or_set(self):
        self.assertIsNone(cache.get('projector'))
        self.assertEqual(cache.get_or_set('projector', 42), 42)
        self.assertEqual(cache.get('projector'), 42)
        self.assertIsNone(cache.get_or_set('null', None))
        if self.supports_get_with_default:
            # Previous get_or_set() stores None in the cache.
            self.assertIsNone(cache.get('null', 'default'))
        else:
            self.assertEqual(cache.get('null', 'default'), 'default')

    def test_get_or_set_callable(self):
        def my_callable():
            return 'value'

        self.assertEqual(cache.get_or_set('mykey', my_callable), 'value')
        self.assertEqual(cache.get_or_set('mykey', my_callable()), 'value')

        self.assertIsNone(cache.get_or_set('null', lambda: None))
        if self.supports_get_with_default:
            # Previous get_or_set() stores None in the cache.
            self.assertIsNone(cache.get('null', 'default'))
        else:
            self.assertEqual(cache.get('null', 'default'), 'default')

    def test_get_or_set_version(self):
        msg = "get_or_set() missing 1 required positional argument: 'default'"
        self.assertEqual(cache.get_or_set('brian', 1979, version=2), 1979)
        with self.assertRaisesMessage(TypeError, msg):
            cache.get_or_set('brian')
        with self.assertRaisesMessage(TypeError, msg):
            cache.get_or_set('brian', version=1)
        self.assertIsNone(cache.get('brian', version=1))
        self.assertEqual(cache.get_or_set('brian', 42, version=1), 42)
        self.assertEqual(cache.get_or_set('brian', 1979, version=2), 1979)
        self.assertIsNone(cache.get('brian', version=3))

    def test_get_or_set_racing(self):
        with mock.patch('%s.%s' % (settings.CACHES['default']['BACKEND'], 'add')) as cache_add:
            # Simulate cache.add() failing to add a value. In that case, the
            # default value should be returned.
            cache_add.return_value = False
            self.assertEqual(cache.get_or_set('key', 'default'), 'default')


@override_settings(CACHES=caches_setting_for_tests(
    BACKEND='django.core.cache.backends.db.DatabaseCache',
    # Spaces are used in the table name to ensure quoting/escaping is working
    LOCATION='test cache table'
))
class DBCacheTests(BaseCacheTests, TransactionTestCase):

    available_apps = ['cache']

    def setUp(self):
        # The super calls needs to happen first for the settings override.
        super().setUp()
        self.create_table()

    def tearDown(self):
        # The super call needs to happen first because it uses the database.
        super().tearDown()
        self.drop_table()

    def create_table(self):
        management.call_command('createcachetable', verbosity=0)

    def drop_table(self):
        with connection.cursor() as cursor:
            table_name = connection.ops.quote_name('test cache table')
            cursor.execute('DROP TABLE %s' % table_name)

    def test_get_many_num_queries(self):
        cache.set_many({'a': 1, 'b': 2})
        cache.set('expired', 'expired', 0.01)
        with self.assertNumQueries(1):
            self.assertEqual(cache.get_many(['a', 'b']), {'a': 1, 'b': 2})
        time.sleep(0.02)
        with self.assertNumQueries(2):
            self.assertEqual(cache.get_many(['a', 'b', 'expired']), {'a': 1, 'b': 2})

    def test_delete_many_num_queries(self):
        cache.set_many({'a': 1, 'b': 2, 'c': 3})
        with self.assertNumQueries(1):
            cache.delete_many(['a', 'b', 'c'])

    def test_zero_cull(self):
        self._perform_cull_test('zero_cull', 50, 18)

    def test_second_call_doesnt_crash(self):
        out = io.StringIO()
        management.call_command('createcachetable', stdout=out)
        self.assertEqual(out.getvalue(), "Cache table 'test cache table' already exists.\n" * len(settings.CACHES))

    @override_settings(CACHES=caches_setting_for_tests(
        BACKEND='django.core.cache.backends.db.DatabaseCache',
        # Use another table name to avoid the 'table already exists' message.
        LOCATION='createcachetable_dry_run_mode'
    ))
    def test_createcachetable_dry_run_mode(self):
        out = io.StringIO()
        management.call_command('createcachetable', dry_run=True, stdout=out)
        output = out.getvalue()
        self.assertTrue(output.startswith("CREATE TABLE"))

    def test_createcachetable_with_table_argument(self):
        """
        Delete and recreate cache table with legacy behavior (explicitly
        specifying the table name).
        """
        self.drop_table()
        out = io.StringIO()
        management.call_command(
            'createcachetable',
            'test cache table',
            verbosity=2,
            stdout=out,
        )
        self.assertEqual(out.getvalue(), "Cache table 'test cache table' created.\n")


@override_settings(USE_TZ=True)
class DBCacheWithTimeZoneTests(DBCacheTests):
    pass


class DBCacheRouter:
    """A router that puts the cache table on the 'other' database."""

    def db_for_read(self, model, **hints):
        if model._meta.app_label == 'django_cache':
            return 'other'
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label == 'django_cache':
            return 'other'
        return None

    def allow_migrate(self, db, app_label, **hints):
        if app_label == 'django_cache':
            return db == 'other'
        return None


@override_settings(
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.db.DatabaseCache',
            'LOCATION': 'my_cache_table',
        },
    },
)
class CreateCacheTableForDBCacheTests(TestCase):
    databases = {'default', 'other'}

    @override_settings(DATABASE_ROUTERS=[DBCacheRouter()])
    def test_createcachetable_observes_database_router(self):
        # cache table should not be created on 'default'
        with self.assertNumQueries(0, using='default'):
            management.call_command('createcachetable', database='default', verbosity=0)
        # cache table should be created on 'other'
        # Queries:
        #   1: check table doesn't already exist
        #   2: create savepoint (if transactional DDL is supported)
        #   3: create the table
        #   4: create the index
        #   5: release savepoint (if transactional DDL is supported)
        num = 5 if connections['other'].features.can_rollback_ddl else 3
        with self.assertNumQueries(num, using='other'):
            management.call_command('createcachetable', database='other', verbosity=0)


class PicklingSideEffect:

    def __init__(self, cache):
        self.cache = cache
        self.locked = False

    def __getstate__(self):
        self.locked = self.cache._lock.locked()
        return {}


limit_locmem_entries = override_settings(CACHES=caches_setting_for_tests(
    BACKEND='django.core.cache.backends.locmem.LocMemCache',
    OPTIONS={'MAX_ENTRIES': 9},
))


@override_settings(CACHES=caches_setting_for_tests(
    BACKEND='django.core.cache.backends.locmem.LocMemCache',
))
class LocMemCacheTests(BaseCacheTests, TestCase):

    def setUp(self):
        super().setUp()

        # LocMem requires a hack to make the other caches
        # share a data store with the 'normal' cache.
        caches['prefix']._cache = cache._cache
        caches['prefix']._expire_info = cache._expire_info

        caches['v2']._cache = cache._cache
        caches['v2']._expire_info = cache._expire_info

        caches['custom_key']._cache = cache._cache
        caches['custom_key']._expire_info = cache._expire_info

        caches['custom_key2']._cache = cache._cache
        caches['custom_key2']._expire_info = cache._expire_info

    @override_settings(CACHES={
        'default': {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache'},
        'other': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
            'LOCATION': 'other'
        },
    })
    def test_multiple_caches(self):
        "Multiple locmem caches are isolated"
        cache.set('value', 42)
        self.assertEqual(caches['default'].get('value'), 42)
        self.assertIsNone(caches['other'].get('value'))

    def test_locking_on_pickle(self):
        """#20613/#18541 -- Ensures pickling is done outside of the lock."""
        bad_obj = PicklingSideEffect(cache)
        cache.set('set', bad_obj)
        self.assertFalse(bad_obj.locked, "Cache was locked during pickling")

        self.assertIs(cache.add('add', bad_obj), True)
        self.assertFalse(bad_obj.locked, "Cache was locked during pickling")

    def test_incr_decr_timeout(self):
        """incr/decr does not modify expiry time (matches memcached behavior)"""
        key = 'value'
        _key = cache.make_key(key)
        cache.set(key, 1, timeout=cache.default_timeout * 10)
        expire = cache._expire_info[_key]
        self.assertEqual(cache.incr(key), 2)
        self.assertEqual(expire, cache._expire_info[_key])
        self.assertEqual(cache.decr(key), 1)
        self.assertEqual(expire, cache._expire_info[_key])

    @limit_locmem_entries
    def test_lru_get(self):
        """get() moves cache keys."""
        for key in range(9):
            cache.set(key, key, timeout=None)
        for key in range(6):
            self.assertEqual(cache.get(key), key)
        cache.set(9, 9, timeout=None)
        for key in range(6):
            self.assertEqual(cache.get(key), key)
        for key in range(6, 9):
            self.assertIsNone(cache.get(key))
        self.assertEqual(cache.get(9), 9)

    @limit_locmem_entries
    def test_lru_set(self):
        """set() moves cache keys."""
        for key in range(9):
            cache.set(key, key, timeout=None)
        for key in range(3, 9):
            cache.set(key, key, timeout=None)
        cache.set(9, 9, timeout=None)
        for key in range(3, 10):
            self.assertEqual(cache.get(key), key)
        for key in range(3):
            self.assertIsNone(cache.get(key))

    @limit_locmem_entries
    def test_lru_incr(self):
        """incr() moves cache keys."""
        for key in range(9):
            cache.set(key, key, timeout=None)
        for key in range(6):
            self.assertEqual(cache.incr(key), key + 1)
        cache.set(9, 9, timeout=None)
        for key in range(6):
            self.assertEqual(cache.get(key), key + 1)
        for key in range(6, 9):
            self.assertIsNone(cache.get(key))
        self.assertEqual(cache.get(9), 9)


# memcached backend isn't guaranteed to be available.
# To check the memcached backend, the test settings file will
# need to contain at least one cache backend setting that points at
# your memcache server.
configured_caches = {}
for _cache_params in settings.CACHES.values():
    configured_caches[_cache_params['BACKEND']] = _cache_params

PyLibMCCache_params = configured_caches.get('django.core.cache.backends.memcached.PyLibMCCache')
PyMemcacheCache_params = configured_caches.get('django.core.cache.backends.memcached.PyMemcacheCache')

# The memcached backends don't support cull-related options like `MAX_ENTRIES`.
memcached_excluded_caches = {'cull', 'zero_cull'}


class BaseMemcachedTests(BaseCacheTests):

    # By default it's assumed that the client doesn't clean up connections
    # properly, in which case the backend must do so after each request.
    should_disconnect_on_close = True

    def test_location_multiple_servers(self):
        locations = [
            ['server1.tld', 'server2:11211'],
            'server1.tld;server2:11211',
            'server1.tld,server2:11211',
        ]
        for location in locations:
            with self.subTest(location=location):
                params = {'BACKEND': self.base_params['BACKEND'], 'LOCATION': location}
                with self.settings(CACHES={'default': params}):
                    self.assertEqual(cache._servers, ['server1.tld', 'server2:11211'])

    def _perform_invalid_key_test(self, key, expected_warning):
        """
        While other backends merely warn, memcached should raise for an invalid
        key.
        """
        msg = expected_warning.replace(key, cache.make_key(key))
        tests = [
            ('add', [key, 1]),
            ('get', [key]),
            ('set', [key, 1]),
            ('incr', [key]),
            ('decr', [key]),
            ('touch', [key]),
            ('delete', [key]),
            ('get_many', [[key, 'b']]),
            ('set_many', [{key: 1, 'b': 2}]),
            ('delete_many', [{key: 1, 'b': 2}]),
        ]
        for operation, args in tests:
            with self.subTest(operation=operation):
                with self.assertRaises(InvalidCacheKey) as cm:
                    getattr(cache, operation)(*args)
                self.assertEqual(str(cm.exception), msg)

    def test_default_never_expiring_timeout(self):
        # Regression test for #22845
        with self.settings(CACHES=caches_setting_for_tests(
                base=self.base_params,
                exclude=memcached_excluded_caches,
                TIMEOUT=None)):
            cache.set('infinite_foo', 'bar')
            self.assertEqual(cache.get('infinite_foo'), 'bar')

    def test_default_far_future_timeout(self):
        # Regression test for #22845
        with self.settings(CACHES=caches_setting_for_tests(
                base=self.base_params,
                exclude=memcached_excluded_caches,
                # 60*60*24*365, 1 year
                TIMEOUT=31536000)):
            cache.set('future_foo', 'bar')
            self.assertEqual(cache.get('future_foo'), 'bar')

    def test_memcached_deletes_key_on_failed_set(self):
        # By default memcached allows objects up to 1MB. For the cache_db session
        # backend to always use the current session, memcached needs to delete
        # the old key if it fails to set.
        max_value_length = 2 ** 20

        cache.set('small_value', 'a')
        self.assertEqual(cache.get('small_value'), 'a')

        large_value = 'a' * (max_value_length + 1)
        try:
            cache.set('small_value', large_value)
        except Exception:
            # Most clients (e.g. pymemcache or pylibmc) raise when the value is
            # too large. This test is primarily checking that the key was
            # deleted, so the return/exception behavior for the set() itself is
            # not important.
            pass
        # small_value should be deleted, or set if configured to accept larger values
        value = cache.get('small_value')
        self.assertTrue(value is None or value == large_value)

    def test_close(self):
        # For clients that don't manage their connections properly, the
        # connection is closed when the request is complete.
        signals.request_finished.disconnect(close_old_connections)
        try:
            with mock.patch.object(cache._class, 'disconnect_all', autospec=True) as mock_disconnect:
                signals.request_finished.send(self.__class__)
                self.assertIs(mock_disconnect.called, self.should_disconnect_on_close)
        finally:
            signals.request_finished.connect(close_old_connections)

    def test_set_many_returns_failing_keys(self):
        def fail_set_multi(mapping, *args, **kwargs):
            return mapping.keys()
        with mock.patch.object(cache._class, 'set_multi', side_effect=fail_set_multi):
            failing_keys = cache.set_many({'key': 'value'})
            self.assertEqual(failing_keys, ['key'])


# RemovedInDjango41Warning.
MemcachedCache_params = configured_caches.get('django.core.cache.backends.memcached.MemcachedCache')


@ignore_warnings(category=RemovedInDjango41Warning)
@unittest.skipUnless(MemcachedCache_params, "MemcachedCache backend not configured")
@override_settings(CACHES=caches_setting_for_tests(
    base=MemcachedCache_params,
    exclude=memcached_excluded_caches,
))
class MemcachedCacheTests(BaseMemcachedTests, TestCase):
    base_params = MemcachedCache_params
    supports_get_with_default = False
    incr_decr_type_error = ValueError

    def test_memcached_uses_highest_pickle_version(self):
        # Regression test for #19810
        for cache_key in settings.CACHES:
            with self.subTest(cache_key=cache_key):
                self.assertEqual(caches[cache_key]._cache.pickleProtocol, pickle.HIGHEST_PROTOCOL)

    @override_settings(CACHES=caches_setting_for_tests(
        base=MemcachedCache_params,
        exclude=memcached_excluded_caches,
        OPTIONS={'server_max_value_length': 9999},
    ))
    def test_memcached_options(self):
        self.assertEqual(cache._cache.server_max_value_length, 9999)

    def test_default_used_when_none_is_set(self):
        """
        python-memcached doesn't support default in get() so this test
        overrides the one in BaseCacheTests.
        """
        cache.set('key_default_none', None)
        self.assertEqual(cache.get('key_default_none', default='default'), 'default')


class MemcachedCacheDeprecationTests(SimpleTestCase):
    def test_warning(self):
        from django.core.cache.backends.memcached import MemcachedCache

        # Remove warnings filter on MemcachedCache deprecation warning, added
        # in runtests.py.
        warnings.filterwarnings(
            'error',
            'MemcachedCache is deprecated',
            category=RemovedInDjango41Warning,
        )
        try:
            msg = (
                'MemcachedCache is deprecated in favor of PyMemcacheCache and '
                'PyLibMCCache.'
            )
            with self.assertRaisesMessage(RemovedInDjango41Warning, msg):
                MemcachedCache('127.0.0.1:11211', {})
        finally:
            warnings.filterwarnings(
                'ignore',
                'MemcachedCache is deprecated',
                category=RemovedInDjango41Warning,
            )


@unittest.skipUnless(PyLibMCCache_params, "PyLibMCCache backend not configured")
@override_settings(CACHES=caches_setting_for_tests(
    base=PyLibMCCache_params,
    exclude=memcached_excluded_caches,
))
class PyLibMCCacheTests(BaseMemcachedTests, TestCase):
    base_params = PyLibMCCache_params
    # libmemcached manages its own connections.
    should_disconnect_on_close = False

    @property
    def incr_decr_type_error(self):
        return cache._lib.ClientError

    @override_settings(CACHES=caches_setting_for_tests(
        base=PyLibMCCache_params,
        exclude=memcached_excluded_caches,
        OPTIONS={
            'binary': True,
            'behaviors': {'tcp_nodelay': True},
        },
    ))
    def test_pylibmc_options(self):
        self.assertTrue(cache._cache.binary)
        self.assertEqual(cache._cache.behaviors['tcp_nodelay'], int(True))

    def test_pylibmc_client_servers(self):
        backend = self.base_params['BACKEND']
        tests = [
            ('unix:/run/memcached/socket', '/run/memcached/socket'),
            ('/run/memcached/socket', '/run/memcached/socket'),
            ('localhost', 'localhost'),
            ('localhost:11211', 'localhost:11211'),
            ('[::1]', '[::1]'),
            ('[::1]:11211', '[::1]:11211'),
            ('127.0.0.1', '127.0.0.1'),
            ('127.0.0.1:11211', '127.0.0.1:11211'),
        ]
        for location, expected in tests:
            settings = {'default': {'BACKEND': backend, 'LOCATION': location}}
            with self.subTest(location), self.settings(CACHES=settings):
                self.assertEqual(cache.client_servers, [expected])


@unittest.skipUnless(PyMemcacheCache_params, 'PyMemcacheCache backend not configured')
@override_settings(CACHES=caches_setting_for_tests(
    base=PyMemcacheCache_params,
    exclude=memcached_excluded_caches,
))
class PyMemcacheCacheTests(BaseMemcachedTests, TestCase):
    base_params = PyMemcacheCache_params

    @property
    def incr_decr_type_error(self):
        return cache._lib.exceptions.MemcacheClientError

    def test_pymemcache_highest_pickle_version(self):
        self.assertEqual(
            cache._cache.default_kwargs['serde']._serialize_func.keywords['pickle_version'],
            pickle.HIGHEST_PROTOCOL,
        )
        for cache_key in settings.CACHES:
            for client_key, client in caches[cache_key]._cache.clients.items():
                with self.subTest(cache_key=cache_key, server=client_key):
                    self.assertEqual(
                        client.serde._serialize_func.keywords['pickle_version'],
                        pickle.HIGHEST_PROTOCOL,
                    )

    @override_settings(CACHES=caches_setting_for_tests(
        base=PyMemcacheCache_params,
        exclude=memcached_excluded_caches,
        OPTIONS={'no_delay': True},
    ))
    def test_pymemcache_options(self):
        self.assertIs(cache._cache.default_kwargs['no_delay'], True)


@override_settings(CACHES=caches_setting_for_tests(
    BACKEND='django.core.cache.backends.filebased.FileBasedCache',
))
class FileBasedCacheTests(BaseCacheTests, TestCase):
    """
    Specific test cases for the file-based cache.
    """

    def setUp(self):
        super().setUp()
        self.dirname = self.mkdtemp()
        # Caches location cannot be modified through override_settings / modify_settings,
        # hence settings are manipulated directly here and the setting_changed signal
        # is triggered manually.
        for cache_params in settings.CACHES.values():
            cache_params['LOCATION'] = self.dirname
        setting_changed.send(self.__class__, setting='CACHES', enter=False)

    def tearDown(self):
        super().tearDown()
        # Call parent first, as cache.clear() may recreate cache base directory
        shutil.rmtree(self.dirname)

    def mkdtemp(self):
        return tempfile.mkdtemp()

    def test_ignores_non_cache_files(self):
        fname = os.path.join(self.dirname, 'not-a-cache-file')
        with open(fname, 'w'):
            os.utime(fname, None)
        cache.clear()
        self.assertTrue(os.path.exists(fname),
                        'Expected cache.clear to ignore non cache files')
        os.remove(fname)

    def test_clear_does_not_remove_cache_dir(self):
        cache.clear()
        self.assertTrue(os.path.exists(self.dirname),
                        'Expected cache.clear to keep the cache dir')

    def test_creates_cache_dir_if_nonexistent(self):
        os.rmdir(self.dirname)
        cache.set('foo', 'bar')
        self.assertTrue(os.path.exists(self.dirname))

    def test_get_ignores_enoent(self):
        cache.set('foo', 'bar')
        os.unlink(cache._key_to_file('foo'))
        # Returns the default instead of erroring.
        self.assertEqual(cache.get('foo', 'baz'), 'baz')

    @skipIf(
        sys.platform == 'win32',
        'Windows only partially supports umasks and chmod.',
    )
    def test_cache_dir_permissions(self):
        os.rmdir(self.dirname)
        dir_path = Path(self.dirname) / 'nested' / 'filebasedcache'
        for cache_params in settings.CACHES.values():
            cache_params['LOCATION'] = dir_path
        setting_changed.send(self.__class__, setting='CACHES', enter=False)
        cache.set('foo', 'bar')
        self.assertIs(dir_path.exists(), True)
        tests = [
            dir_path,
            dir_path.parent,
            dir_path.parent.parent,
        ]
        for directory in tests:
            with self.subTest(directory=directory):
                dir_mode = directory.stat().st_mode & 0o777
                self.assertEqual(dir_mode, 0o700)

    def test_get_does_not_ignore_non_filenotfound_exceptions(self):
        with mock.patch('builtins.open', side_effect=OSError):
            with self.assertRaises(OSError):
                cache.get('foo')

    def test_empty_cache_file_considered_expired(self):
        cache_file = cache._key_to_file('foo')
        with open(cache_file, 'wb') as fh:
            fh.write(b'')
        with open(cache_file, 'rb') as fh:
            self.assertIs(cache._is_expired(fh), True)


class FileBasedCachePathLibTests(FileBasedCacheTests):
    def mkdtemp(self):
        tmp_dir = super().mkdtemp()
        return Path(tmp_dir)


@override_settings(CACHES={
    'default': {
        'BACKEND': 'cache.liberal_backend.CacheClass',
    },
})
class CustomCacheKeyValidationTests(SimpleTestCase):
    """
    Tests for the ability to mixin a custom ``validate_key`` method to
    a custom cache backend that otherwise inherits from a builtin
    backend, and override the default key validation. Refs #6447.
    """
    def test_custom_key_validation(self):
        # this key is both longer than 250 characters, and has spaces
        key = 'some key with spaces' * 15
        val = 'a value'
        cache.set(key, val)
        self.assertEqual(cache.get(key), val)


@override_settings(
    CACHES={
        'default': {
            'BACKEND': 'cache.closeable_cache.CacheClass',
        }
    }
)
class CacheClosingTests(SimpleTestCase):

    def test_close(self):
        self.assertFalse(cache.closed)
        signals.request_finished.send(self.__class__)
        self.assertTrue(cache.closed)


DEFAULT_MEMORY_CACHES_SETTINGS = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'unique-snowflake',
    }
}
NEVER_EXPIRING_CACHES_SETTINGS = copy.deepcopy(DEFAULT_MEMORY_CACHES_SETTINGS)
NEVER_EXPIRING_CACHES_SETTINGS['default']['TIMEOUT'] = None


class DefaultNonExpiringCacheKeyTests(SimpleTestCase):
    """
    Settings having Cache arguments with a TIMEOUT=None create Caches that will
    set non-expiring keys.
    """
    def setUp(self):
        # The 5 minute (300 seconds) default expiration time for keys is
        # defined in the implementation of the initializer method of the
        # BaseCache type.
        self.DEFAULT_TIMEOUT = caches[DEFAULT_CACHE_ALIAS].default_timeout

    def tearDown(self):
        del(self.DEFAULT_TIMEOUT)

    def test_default_expiration_time_for_keys_is_5_minutes(self):
        """The default expiration time of a cache key is 5 minutes.

        This value is defined in
        django.core.cache.backends.base.BaseCache.__init__().
        """
        self.assertEqual(300, self.DEFAULT_TIMEOUT)

    def test_caches_with_unset_timeout_has_correct_default_timeout(self):
        """Caches that have the TIMEOUT parameter undefined in the default
        settings will use the default 5 minute timeout.
        """
        cache = caches[DEFAULT_CACHE_ALIAS]
        self.assertEqual(self.DEFAULT_TIMEOUT, cache.default_timeout)

    @override_settings(CACHES=NEVER_EXPIRING_CACHES_SETTINGS)
    def test_caches_set_with_timeout_as_none_has_correct_default_timeout(self):
        """Memory caches that have the TIMEOUT parameter set to `None` in the
        default settings with have `None` as the default timeout.

        This means "no timeout".
        """
        cache = caches[DEFAULT_CACHE_ALIAS]
        self.assertIsNone(cache.default_timeout)
        self.assertIsNone(cache.get_backend_timeout())

    @override_settings(CACHES=DEFAULT_MEMORY_CACHES_SETTINGS)
    def test_caches_with_unset_timeout_set_expiring_key(self):
        """Memory caches that have the TIMEOUT parameter unset will set cache
        keys having the default 5 minute timeout.
        """
        key = "my-key"
        value = "my-value"
        cache = caches[DEFAULT_CACHE_ALIAS]
        cache.set(key, value)
        cache_key = cache.make_key(key)
        self.assertIsNotNone(cache._expire_info[cache_key])

    @override_settings(CACHES=NEVER_EXPIRING_CACHES_SETTINGS)
    def test_caches_set_with_timeout_as_none_set_non_expiring_key(self):
        """Memory caches that have the TIMEOUT parameter set to `None` will set
        a non expiring key by default.
        """
        key = "another-key"
        value = "another-value"
        cache = caches[DEFAULT_CACHE_ALIAS]
        cache.set(key, value)
        cache_key = cache.make_key(key)
        self.assertIsNone(cache._expire_info[cache_key])


@override_settings(
    CACHE_MIDDLEWARE_KEY_PREFIX='settingsprefix',
    CACHE_MIDDLEWARE_SECONDS=1,
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        },
    },
    USE_I18N=False,
    ALLOWED_HOSTS=['.example.com'],
)
class CacheUtils(SimpleTestCase):
    """TestCase for django.utils.cache functions."""
    host = 'www.example.com'
    path = '/cache/test/'
    factory = RequestFactory(HTTP_HOST=host)

    def tearDown(self):
        cache.clear()

    def _get_request_cache(self, method='GET', query_string=None, update_cache=None):
        request = self._get_request(self.host, self.path,
                                    method, query_string=query_string)
        request._cache_update_cache = update_cache if update_cache else True
        return request

    def test_patch_vary_headers(self):
        headers = (
            # Initial vary, new headers, resulting vary.
            (None, ('Accept-Encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('accept-encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('ACCEPT-ENCODING',), 'Accept-Encoding'),
            ('Cookie', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            (None, ('Accept-Encoding', 'COOKIE'), 'Accept-Encoding, COOKIE'),
            ('Cookie,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            ('Cookie    ,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            ('*', ('Accept-Language', 'Cookie'), '*'),
            ('Accept-Language, Cookie', ('*',), '*'),
        )
        for initial_vary, newheaders, resulting_vary in headers:
            with self.subTest(initial_vary=initial_vary, newheaders=newheaders):
                response = HttpResponse()
                if initial_vary is not None:
                    response.headers['Vary'] = initial_vary
                patch_vary_headers(response, newheaders)
                self.assertEqual(response.headers['Vary'], resulting_vary)

    def test_get_cache_key(self):
        request = self.factory.get(self.path)
        response = HttpResponse()
        # Expect None if no headers have been set yet.
        self.assertIsNone(get_cache_key(request))
        # Set headers to an empty list.
        learn_cache_key(request, response)

        self.assertEqual(
            get_cache_key(request),
            'views.decorators.cache.cache_page.settingsprefix.GET.'
            '18a03f9c9649f7d684af5db3524f5c99.d41d8cd98f00b204e9800998ecf8427e'
        )
        # A specified key_prefix is taken into account.
        key_prefix = 'localprefix'
        learn_cache_key(request, response, key_prefix=key_prefix)
        self.assertEqual(
            get_cache_key(request, key_prefix=key_prefix),
            'views.decorators.cache.cache_page.localprefix.GET.'
            '18a03f9c9649f7d684af5db3524f5c99.d41d8cd98f00b204e9800998ecf8427e'
        )

    def test_get_cache_key_with_query(self):
        request = self.factory.get(self.path, {'test': 1})
        response = HttpResponse()
        # Expect None if no headers have been set yet.
        self.assertIsNone(get_cache_key(request))
        # Set headers to an empty list.
        learn_cache_key(request, response)
        # The querystring is taken into account.
        self.assertEqual(
            get_cache_key(request),
            'views.decorators.cache.cache_page.settingsprefix.GET.'
            'beaf87a9a99ee81c673ea2d67ccbec2a.d41d8cd98f00b204e9800998ecf8427e'
        )

    def test_cache_key_varies_by_url(self):
        """
        get_cache_key keys differ by fully-qualified URL instead of path
        """
        request1 = self.factory.get(self.path, HTTP_HOST='sub-1.example.com')
        learn_cache_key(request1, HttpResponse())
        request2 = self.factory.get(self.path, HTTP_HOST='sub-2.example.com')
        learn_cache_key(request2, HttpResponse())
        self.assertNotEqual(get_cache_key(request1), get_cache_key(request2))

    def test_learn_cache_key(self):
        request = self.factory.head(self.path)
        response = HttpResponse()
        response.headers['Vary'] = 'Pony'
        # Make sure that the Vary header is added to the key hash
        learn_cache_key(request, response)

        self.assertEqual(
            get_cache_key(request),
            'views.decorators.cache.cache_page.settingsprefix.GET.'
            '18a03f9c9649f7d684af5db3524f5c99.d41d8cd98f00b204e9800998ecf8427e'
        )

    def test_patch_cache_control(self):
        tests = (
            # Initial Cache-Control, kwargs to patch_cache_control, expected Cache-Control parts
            (None, {'private': True}, {'private'}),
            ('', {'private': True}, {'private'}),
            # no-cache.
            ('', {'no_cache': 'Set-Cookie'}, {'no-cache=Set-Cookie'}),
            ('', {'no-cache': 'Set-Cookie'}, {'no-cache=Set-Cookie'}),
            ('no-cache=Set-Cookie', {'no_cache': True}, {'no-cache'}),
            ('no-cache=Set-Cookie,no-cache=Link', {'no_cache': True}, {'no-cache'}),
            ('no-cache=Set-Cookie', {'no_cache': 'Link'}, {'no-cache=Set-Cookie', 'no-cache=Link'}),
            (
                'no-cache=Set-Cookie,no-cache=Link',
                {'no_cache': 'Custom'},
                {'no-cache=Set-Cookie', 'no-cache=Link', 'no-cache=Custom'},
            ),
            # Test whether private/public attributes are mutually exclusive
            ('private', {'private': True}, {'private'}),
            ('private', {'public': True}, {'public'}),
            ('public', {'public': True}, {'public'}),
            ('public', {'private': True}, {'private'}),
            ('must-revalidate,max-age=60,private', {'public': True}, {'must-revalidate', 'max-age=60', 'public'}),
            ('must-revalidate,max-age=60,public', {'private': True}, {'must-revalidate', 'max-age=60', 'private'}),
            ('must-revalidate,max-age=60', {'public': True}, {'must-revalidate', 'max-age=60', 'public'}),
        )

        cc_delim_re = re.compile(r'\s*,\s*')

        for initial_cc, newheaders, expected_cc in tests:
            with self.subTest(initial_cc=initial_cc, newheaders=newheaders):
                response = HttpResponse()
                if initial_cc is not None:
                    response.headers['Cache-Control'] = initial_cc
                patch_cache_control(response, **newheaders)
                parts = set(cc_delim_re.split(response.headers['Cache-Control']))
                self.assertEqual(parts, expected_cc)


@override_settings(
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
            'KEY_PREFIX': 'cacheprefix',
        },
    },
)
class PrefixedCacheUtils(CacheUtils):
    pass


@override_settings(
    CACHE_MIDDLEWARE_SECONDS=60,
    CACHE_MIDDLEWARE_KEY_PREFIX='test',
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        },
    },
)
class CacheHEADTest(SimpleTestCase):
    path = '/cache/test/'
    factory = RequestFactory()

    def tearDown(self):
        cache.clear()

    def _set_cache(self, request, msg):
        return UpdateCacheMiddleware(lambda req: HttpResponse(msg))(request)

    def test_head_caches_correctly(self):
        test_content = 'test content'

        request = self.factory.head(self.path)
        request._cache_update_cache = True
        self._set_cache(request, test_content)

        request = self.factory.head(self.path)
        request._cache_update_cache = True
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(test_content.encode(), get_cache_data.content)

    def test_head_with_cached_get(self):
        test_content = 'test content'

        request = self.factory.get(self.path)
        request._cache_update_cache = True
        self._set_cache(request, test_content)

        request = self.factory.head(self.path)
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(test_content.encode(), get_cache_data.content)


@override_settings(
    CACHE_MIDDLEWARE_KEY_PREFIX='settingsprefix',
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        },
    },
    LANGUAGES=[
        ('en', 'English'),
        ('es', 'Spanish'),
    ],
)
class CacheI18nTest(SimpleTestCase):
    path = '/cache/test/'
    factory = RequestFactory()

    def tearDown(self):
        cache.clear()

    @override_settings(USE_I18N=True, USE_TZ=False)
    def test_cache_key_i18n_translation(self):
        request = self.factory.get(self.path)
        lang = translation.get_language()
        response = HttpResponse()
        key = learn_cache_key(request, response)
        self.assertIn(lang, key, "Cache keys should include the language name when translation is active")
        key2 = get_cache_key(request)
        self.assertEqual(key, key2)

    def check_accept_language_vary(self, accept_language, vary, reference_key):
        request = self.factory.get(self.path)
        request.META['HTTP_ACCEPT_LANGUAGE'] = accept_language
        request.META['HTTP_ACCEPT_ENCODING'] = 'gzip;q=1.0, identity; q=0.5, *;q=0'
        response = HttpResponse()
        response.headers['Vary'] = vary
        key = learn_cache_key(request, response)
        key2 = get_cache_key(request)
        self.assertEqual(key, reference_key)
        self.assertEqual(key2, reference_key)

    @override_settings(USE_I18N=True, USE_TZ=False)
    def test_cache_key_i18n_translation_accept_language(self):
        lang = translation.get_language()
        self.assertEqual(lang, 'en')
        request = self.factory.get(self.path)
        request.META['HTTP_ACCEPT_ENCODING'] = 'gzip;q=1.0, identity; q=0.5, *;q=0'
        response = HttpResponse()
        response.headers['Vary'] = 'accept-encoding'
        key = learn_cache_key(request, response)
        self.assertIn(lang, key, "Cache keys should include the language name when translation is active")
        self.check_accept_language_vary(
            'en-us',
            'cookie, accept-language, accept-encoding',
            key
        )
        self.check_accept_language_vary(
            'en-US',
            'cookie, accept-encoding, accept-language',
            key
        )
        self.check_accept_language_vary(
            'en-US,en;q=0.8',
            'accept-encoding, accept-language, cookie',
            key
        )
        self.check_accept_language_vary(
            'en-US,en;q=0.8,ko;q=0.6',
            'accept-language, cookie, accept-encoding',
            key
        )
        self.check_accept_language_vary(
            'ko-kr,ko;q=0.8,en-us;q=0.5,en;q=0.3 ',
            'accept-encoding, cookie, accept-language',
            key
        )
        self.check_accept_language_vary(
            'ko-KR,ko;q=0.8,en-US;q=0.6,en;q=0.4',
            'accept-language, accept-encoding, cookie',
            key
        )
        self.check_accept_language_vary(
            'ko;q=1.0,en;q=0.5',
            'cookie, accept-language, accept-encoding',
            key
        )
        self.check_accept_language_vary(
            'ko, en',
            'cookie, accept-encoding, accept-language',
            key
        )
        self.check_accept_language_vary(
            'ko-KR, en-US',
            'accept-encoding, accept-language, cookie',
            key
        )

    @override_settings(USE_I18N=False, USE_TZ=True)
    def test_cache_key_i18n_timezone(self):
        request = self.factory.get(self.path)
        tz = timezone.get_current_timezone_name()
        response = HttpResponse()
        key = learn_cache_key(request, response)
        self.assertIn(tz, key, "Cache keys should include the time zone name when time zones are active")
        key2 = get_cache_key(request)
        self.assertEqual(key, key2)

    @override_settings(USE_I18N=False)
    def test_cache_key_no_i18n(self):
        request = self.factory.get(self.path)
        lang = translation.get_language()
        tz = timezone.get_current_timezone_name()
        response = HttpResponse()
        key = learn_cache_key(request, response)
        self.assertNotIn(lang, key, "Cache keys shouldn't include the language name when i18n isn't active")
        self.assertNotIn(tz, key, "Cache keys shouldn't include the time zone name when i18n isn't active")

    @override_settings(
        CACHE_MIDDLEWARE_KEY_PREFIX="test",
        CACHE_MIDDLEWARE_SECONDS=60,
        USE_I18N=True,
    )
    def test_middleware(self):
        def set_cache(request, lang, msg):
            def get_response(req):
                return HttpResponse(msg)

            translation.activate(lang)
            return UpdateCacheMiddleware(get_response)(request)

        # cache with non empty request.GET
        request = self.factory.get(self.path, {'foo': 'bar', 'other': 'true'})
        request._cache_update_cache = True

        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        # first access, cache must return None
        self.assertIsNone(get_cache_data)
        content = 'Check for cache with QUERY_STRING'

        def get_response(req):
            return HttpResponse(content)

        UpdateCacheMiddleware(get_response)(request)
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        # cache must return content
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(get_cache_data.content, content.encode())
        # different QUERY_STRING, cache must be empty
        request = self.factory.get(self.path, {'foo': 'bar', 'somethingelse': 'true'})
        request._cache_update_cache = True
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNone(get_cache_data)

        # i18n tests
        en_message = "Hello world!"
        es_message = "Hola mundo!"

        request = self.factory.get(self.path)
        request._cache_update_cache = True
        set_cache(request, 'en', en_message)
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        # The cache can be recovered
        self.assertIsNotNone(get_cache_data)
        self.assertEqual(get_cache_data.content, en_message.encode())
        # change the session language and set content
        request = self.factory.get(self.path)
        request._cache_update_cache = True
        set_cache(request, 'es', es_message)
        # change again the language
        translation.activate('en')
        # retrieve the content from cache
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertEqual(get_cache_data.content, en_message.encode())
        # change again the language
        translation.activate('es')
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertEqual(get_cache_data.content, es_message.encode())
        # reset the language
        translation.deactivate()

    @override_settings(
        CACHE_MIDDLEWARE_KEY_PREFIX="test",
        CACHE_MIDDLEWARE_SECONDS=60,
    )
    def test_middleware_doesnt_cache_streaming_response(self):
        request = self.factory.get(self.path)
        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNone(get_cache_data)

        def get_stream_response(req):
            return StreamingHttpResponse(['Check for cache with streaming content.'])

        UpdateCacheMiddleware(get_stream_response)(request)

        get_cache_data = FetchFromCacheMiddleware(empty_response).process_request(request)
        self.assertIsNone(get_cache_data)


@override_settings(
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
            'KEY_PREFIX': 'cacheprefix'
        },
    },
)
class PrefixedCacheI18nTest(CacheI18nTest):
    pass


def hello_world_view(request, value):
    return HttpResponse('Hello World %s' % value)


def csrf_view(request):
    return HttpResponse(csrf(request)['csrf_token'])


@override_settings(
    CACHE_MIDDLEWARE_ALIAS='other',
    CACHE_MIDDLEWARE_KEY_PREFIX='middlewareprefix',
    CACHE_MIDDLEWARE_SECONDS=30,
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        },
        'other': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
            'LOCATION': 'other',
            'TIMEOUT': '1',
        },
    },
)
class CacheMiddlewareTest(SimpleTestCase):
    factory = RequestFactory()

    def setUp(self):
        self.default_cache = caches['default']
        self.other_cache = caches['other']

    def tearDown(self):
        self.default_cache.clear()
        self.other_cache.clear()
        super().tearDown()

    def test_constructor(self):
        """
        Ensure the constructor is correctly distinguishing between usage of CacheMiddleware as
        Middleware vs. usage of CacheMiddleware as view decorator and setting attributes
        appropriately.
        """
        # If only one argument is passed in construction, it's being used as
        # middleware.
        middleware = CacheMiddleware(empty_response)

        # Now test object attributes against values defined in setUp above
        self.assertEqual(middleware.cache_timeout, 30)
        self.assertEqual(middleware.key_prefix, 'middlewareprefix')
        self.assertEqual(middleware.cache_alias, 'other')
        self.assertEqual(middleware.cache, self.other_cache)

        # If more arguments are being passed in construction, it's being used
        # as a decorator. First, test with "defaults":
        as_view_decorator = CacheMiddleware(empty_response, cache_alias=None, key_prefix=None)

        self.assertEqual(as_view_decorator.cache_timeout, 30)  # Timeout value for 'default' cache, i.e. 30
        self.assertEqual(as_view_decorator.key_prefix, '')
        # Value of DEFAULT_CACHE_ALIAS from django.core.cache
        self.assertEqual(as_view_decorator.cache_alias, 'default')
        self.assertEqual(as_view_decorator.cache, self.default_cache)

        # Next, test with custom values:
        as_view_decorator_with_custom = CacheMiddleware(
            hello_world_view, cache_timeout=60, cache_alias='other', key_prefix='foo'
        )

        self.assertEqual(as_view_decorator_with_custom.cache_timeout, 60)
        self.assertEqual(as_view_decorator_with_custom.key_prefix, 'foo')
        self.assertEqual(as_view_decorator_with_custom.cache_alias, 'other')
        self.assertEqual(as_view_decorator_with_custom.cache, self.other_cache)

    def test_update_cache_middleware_constructor(self):
        middleware = UpdateCacheMiddleware(empty_response)
        self.assertEqual(middleware.cache_timeout, 30)
        self.assertIsNone(middleware.page_timeout)
        self.assertEqual(middleware.key_prefix, 'middlewareprefix')
        self.assertEqual(middleware.cache_alias, 'other')
        self.assertEqual(middleware.cache, self.other_cache)

    def test_fetch_cache_middleware_constructor(self):
        middleware = FetchFromCacheMiddleware(empty_response)
        self.assertEqual(middleware.key_prefix, 'middlewareprefix')
        self.assertEqual(middleware.cache_alias, 'other')
        self.assertEqual(middleware.cache, self.other_cache)

    def test_middleware(self):
        middleware = CacheMiddleware(hello_world_view)
        prefix_middleware = CacheMiddleware(hello_world_view, key_prefix='prefix1')
        timeout_middleware = CacheMiddleware(hello_world_view, cache_timeout=1)

        request = self.factory.get('/view/')

        # Put the request through the request middleware
        result = middleware.process_request(request)
        self.assertIsNone(result)

        response = hello_world_view(request, '1')

        # Now put the response through the response middleware
        response = middleware.process_response(request, response)

        # Repeating the request should result in a cache hit
        result = middleware.process_request(request)
        self.assertIsNotNone(result)
        self.assertEqual(result.content, b'Hello World 1')

        # The same request through a different middleware won't hit
        result = prefix_middleware.process_request(request)
        self.assertIsNone(result)

        # The same request with a timeout _will_ hit
        result = timeout_middleware.process_request(request)
        self.assertIsNotNone(result)
        self.assertEqual(result.content, b'Hello World 1')

    def test_view_decorator(self):
        # decorate the same view with different cache decorators
        default_view = cache_page(3)(hello_world_view)
        default_with_prefix_view = cache_page(3, key_prefix='prefix1')(hello_world_view)

        explicit_default_view = cache_page(3, cache='default')(hello_world_view)
        explicit_default_with_prefix_view = cache_page(3, cache='default', key_prefix='prefix1')(hello_world_view)

        other_view = cache_page(1, cache='other')(hello_world_view)
        other_with_prefix_view = cache_page(1, cache='other', key_prefix='prefix2')(hello_world_view)

        request = self.factory.get('/view/')

        # Request the view once
        response = default_view(request, '1')
        self.assertEqual(response.content, b'Hello World 1')

        # Request again -- hit the cache
        response = default_view(request, '2')
        self.assertEqual(response.content, b'Hello World 1')

        # Requesting the same view with the explicit cache should yield the same result
        response = explicit_default_view(request, '3')
        self.assertEqual(response.content, b'Hello World 1')

        # Requesting with a prefix will hit a different cache key
        response = explicit_default_with_prefix_view(request, '4')
        self.assertEqual(response.content, b'Hello World 4')

        # Hitting the same view again gives a cache hit
        response = explicit_default_with_prefix_view(request, '5')
        self.assertEqual(response.content, b'Hello World 4')

        # And going back to the implicit cache will hit the same cache
        response = default_with_prefix_view(request, '6')
        self.assertEqual(response.content, b'Hello World 4')

        # Requesting from an alternate cache won't hit cache
        response = other_view(request, '7')
        self.assertEqual(response.content, b'Hello World 7')

        # But a repeated hit will hit cache
        response = other_view(request, '8')
        self.assertEqual(response.content, b'Hello World 7')

        # And prefixing the alternate cache yields yet another cache entry
        response = other_with_prefix_view(request, '9')
        self.assertEqual(response.content, b'Hello World 9')

        # But if we wait a couple of seconds...
        time.sleep(2)

        # ... the default cache will still hit
        caches['default']
        response = default_view(request, '11')
        self.assertEqual(response.content, b'Hello World 1')

        # ... the default cache with a prefix will still hit
        response = default_with_prefix_view(request, '12')
        self.assertEqual(response.content, b'Hello World 4')

        # ... the explicit default cache will still hit
        response = explicit_default_view(request, '13')
        self.assertEqual(response.content, b'Hello World 1')

        # ... the explicit default cache with a prefix will still hit
        response = explicit_default_with_prefix_view(request, '14')
        self.assertEqual(response.content, b'Hello World 4')

        # .. but a rapidly expiring cache won't hit
        response = other_view(request, '15')
        self.assertEqual(response.content, b'Hello World 15')

        # .. even if it has a prefix
        response = other_with_prefix_view(request, '16')
        self.assertEqual(response.content, b'Hello World 16')

    def test_cache_page_timeout(self):
        # Page timeout takes precedence over the "max-age" section of the
        # "Cache-Control".
        tests = [
            (1, 3),  # max_age < page_timeout.
            (3, 1),  # max_age > page_timeout.
        ]
        for max_age, page_timeout in tests:
            with self.subTest(max_age=max_age, page_timeout=page_timeout):
                view = cache_page(timeout=page_timeout)(
                    cache_control(max_age=max_age)(hello_world_view)
                )
                request = self.factory.get('/view/')
                response = view(request, '1')
                self.assertEqual(response.content, b'Hello World 1')
                time.sleep(1)
                response = view(request, '2')
                self.assertEqual(
                    response.content,
                    b'Hello World 1' if page_timeout > max_age else b'Hello World 2',
                )
            cache.clear()

    def test_cached_control_private_not_cached(self):
        """Responses with 'Cache-Control: private' are not cached."""
        view_with_private_cache = cache_page(3)(cache_control(private=True)(hello_world_view))
        request = self.factory.get('/view/')
        response = view_with_private_cache(request, '1')
        self.assertEqual(response.content, b'Hello World 1')
        response = view_with_private_cache(request, '2')
        self.assertEqual(response.content, b'Hello World 2')

    def test_sensitive_cookie_not_cached(self):
        """
        Django must prevent caching of responses that set a user-specific (and
        maybe security sensitive) cookie in response to a cookie-less request.
        """
        request = self.factory.get('/view/')
        csrf_middleware = CsrfViewMiddleware(csrf_view)
        csrf_middleware.process_view(request, csrf_view, (), {})
        cache_middleware = CacheMiddleware(csrf_middleware)

        self.assertIsNone(cache_middleware.process_request(request))
        cache_middleware(request)

        # Inserting a CSRF cookie in a cookie-less request prevented caching.
        self.assertIsNone(cache_middleware.process_request(request))

    def test_304_response_has_http_caching_headers_but_not_cached(self):
        original_view = mock.Mock(return_value=HttpResponseNotModified())
        view = cache_page(2)(original_view)
        request = self.factory.get('/view/')
        # The view shouldn't be cached on the second call.
        view(request).close()
        response = view(request)
        response.close()
        self.assertEqual(original_view.call_count, 2)
        self.assertIsInstance(response, HttpResponseNotModified)
        self.assertIn('Cache-Control', response)
        self.assertIn('Expires', response)


@override_settings(
    CACHE_MIDDLEWARE_KEY_PREFIX='settingsprefix',
    CACHE_MIDDLEWARE_SECONDS=1,
    CACHES={
        'default': {
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        },
    },
    USE_I18N=False,
)
class TestWithTemplateResponse(SimpleTestCase):
    """
    Tests various headers w/ TemplateResponse.

    Most are probably redundant since they manipulate the same object
    anyway but the ETag header is 'special' because it relies on the
    content being complete (which is not necessarily always the case
    with a TemplateResponse)
    """
    path = '/cache/test/'
    factory = RequestFactory()

    def tearDown(self):
        cache.clear()

    def test_patch_vary_headers(self):
        headers = (
            # Initial vary, new headers, resulting vary.
            (None, ('Accept-Encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('accept-encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('ACCEPT-ENCODING',), 'Accept-Encoding'),
            ('Cookie', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            (None, ('Accept-Encoding', 'COOKIE'), 'Accept-Encoding, COOKIE'),
            ('Cookie,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            ('Cookie    ,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
        )
        for initial_vary, newheaders, resulting_vary in headers:
            with self.subTest(initial_vary=initial_vary, newheaders=newheaders):
                template = engines['django'].from_string("This is a test")
                response = TemplateResponse(HttpRequest(), template)
                if initial_vary is not None:
                    response.headers['Vary'] = initial_vary
                patch_vary_headers(response, newheaders)
                self.assertEqual(response.headers['Vary'], resulting_vary)

    def test_get_cache_key(self):
        request = self.factory.get(self.path)
        template = engines['django'].from_string("This is a test")
        response = TemplateResponse(HttpRequest(), template)
        key_prefix = 'localprefix'
        # Expect None if no headers have been set yet.
        self.assertIsNone(get_cache_key(request))
        # Set headers to an empty list.
        learn_cache_key(request, response)

        self.assertEqual(
            get_cache_key(request),
            'views.decorators.cache.cache_page.settingsprefix.GET.'
            '58a0a05c8a5620f813686ff969c26853.d41d8cd98f00b204e9800998ecf8427e'
        )
        # A specified key_prefix is taken into account.
        learn_cache_key(request, response, key_prefix=key_prefix)
        self.assertEqual(
            get_cache_key(request, key_prefix=key_prefix),
            'views.decorators.cache.cache_page.localprefix.GET.'
            '58a0a05c8a5620f813686ff969c26853.d41d8cd98f00b204e9800998ecf8427e'
        )

    def test_get_cache_key_with_query(self):
        request = self.factory.get(self.path, {'test': 1})
        template = engines['django'].from_string("This is a test")
        response = TemplateResponse(HttpRequest(), template)
        # Expect None if no headers have been set yet.
        self.assertIsNone(get_cache_key(request))
        # Set headers to an empty list.
        learn_cache_key(request, response)
        # The querystring is taken into account.
        self.assertEqual(
            get_cache_key(request),
            'views.decorators.cache.cache_page.settingsprefix.GET.'
            '0f1c2d56633c943073c4569d9a9502fe.d41d8cd98f00b204e9800998ecf8427e'
        )


class TestMakeTemplateFragmentKey(SimpleTestCase):
    def test_without_vary_on(self):
        key = make_template_fragment_key('a.fragment')
        self.assertEqual(key, 'template.cache.a.fragment.d41d8cd98f00b204e9800998ecf8427e')

    def test_with_one_vary_on(self):
        key = make_template_fragment_key('foo', ['abc'])
        self.assertEqual(key, 'template.cache.foo.493e283d571a73056196f1a68efd0f66')

    def test_with_many_vary_on(self):
        key = make_template_fragment_key('bar', ['abc', 'def'])
        self.assertEqual(key, 'template.cache.bar.17c1a507a0cb58384f4c639067a93520')

    def test_proper_escaping(self):
        key = make_template_fragment_key('spam', ['abc:def%'])
        self.assertEqual(key, 'template.cache.spam.06c8ae8e8c430b69fb0a6443504153dc')

    def test_with_ints_vary_on(self):
        key = make_template_fragment_key('foo', [1, 2, 3, 4, 5])
        self.assertEqual(key, 'template.cache.foo.7ae8fd2e0d25d651c683bdeebdb29461')

    def test_with_unicode_vary_on(self):
        key = make_template_fragment_key('foo', ['42º', '😀'])
        self.assertEqual(key, 'template.cache.foo.7ced1c94e543668590ba39b3c08b0237')

    def test_long_vary_on(self):
        key = make_template_fragment_key('foo', ['x' * 10000])
        self.assertEqual(key, 'template.cache.foo.3670b349b5124aa56bdb50678b02b23a')


class CacheHandlerTest(SimpleTestCase):
    def test_same_instance(self):
        """
        Attempting to retrieve the same alias should yield the same instance.
        """
        cache1 = caches['default']
        cache2 = caches['default']

        self.assertIs(cache1, cache2)

    def test_per_thread(self):
        """
        Requesting the same alias from separate threads should yield separate
        instances.
        """
        c = []

        def runner():
            c.append(caches['default'])

        for x in range(2):
            t = threading.Thread(target=runner)
            t.start()
            t.join()

        self.assertIsNot(c[0], c[1])

    def test_nonexistent_alias(self):
        msg = "The connection 'nonexistent' doesn't exist."
        with self.assertRaisesMessage(InvalidCacheBackendError, msg):
            caches['nonexistent']

    def test_nonexistent_backend(self):
        test_caches = CacheHandler({
            'invalid_backend': {
                'BACKEND': 'django.nonexistent.NonexistentBackend',
            },
        })
        msg = (
            "Could not find backend 'django.nonexistent.NonexistentBackend': "
            "No module named 'django.nonexistent'"
        )
        with self.assertRaisesMessage(InvalidCacheBackendError, msg):
            test_caches['invalid_backend']