From cd9fcd4e8073490a52c9e79133ada4661cb7db38 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 5 Feb 2015 20:31:02 +0100
Subject: [PATCH 01/17] Implemented a parallel test runner.

---
 django/test/runner.py     | 234 ++++++++++++++++++++++++++++++++++++--
 docs/ref/django-admin.txt |  20 ++++
 docs/releases/1.9.txt     |   6 +
 tests/runtests.py         |  23 ++--
 4 files changed, 268 insertions(+), 15 deletions(-)

diff --git a/django/test/runner.py b/django/test/runner.py
index 6a8a918984..0ed21fc1c8 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -1,9 +1,10 @@
 import collections
+import itertools
 import logging
+import multiprocessing
 import os
 import unittest
 from importlib import import_module
-from unittest import TestSuite, defaultTestLoader
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
@@ -13,6 +14,11 @@ from django.test.utils import setup_test_environment, teardown_test_environment
 from django.utils.datastructures import OrderedSet
 from django.utils.six import StringIO
 
+try:
+    import tblib.pickling_support
+except ImportError:
+    tblib = None
+
 
 class DebugSQLTextTestResult(unittest.TextTestResult):
     def __init__(self, stream, descriptions, verbosity):
@@ -54,19 +60,206 @@ class DebugSQLTextTestResult(unittest.TextTestResult):
             self.stream.writeln("%s" % sql_debug)
 
 
+class RemoteTestResult(object):
+    """
+    Record information about which tests have succeeded and which have failed.
+
+    The sole purpose of this class is to record events in the child processes
+    so they can be replayed in the master process. As a consequence it doesn't
+    inherit unittest.TestResult and doesn't attempt to implement all its API.
+
+    The implementation matches the unpythonic coding style of unittest2.
+    """
+
+    def __init__(self):
+        self.events = []
+        self.failfast = False
+        self.shouldStop = False
+        self.testsRun = 0
+
+    @property
+    def test_index(self):
+        return self.testsRun - 1
+
+    def stop_if_failfast(self):
+        if self.failfast:
+            self.stop()
+
+    def stop(self):
+        self.shouldStop = True
+
+    def startTestRun(self):
+        self.events.append(('startTestRun',))
+
+    def stopTestRun(self):
+        self.events.append(('stopTestRun',))
+
+    def startTest(self, test):
+        self.testsRun += 1
+        self.events.append(('startTest', self.test_index))
+
+    def stopTest(self, test):
+        self.events.append(('stopTest', self.test_index))
+
+    def addError(self, test, err):
+        self.events.append(('addError', self.test_index, err))
+        self.stop_if_failfast()
+
+    def addFailure(self, test, err):
+        self.events.append(('addFailure', self.test_index, err))
+        self.stop_if_failfast()
+
+    def addSubTest(self, test, subtest, err):
+        raise NotImplementedError("subtests aren't supported at this time")
+
+    def addSuccess(self, test):
+        self.events.append(('addSuccess', self.test_index))
+
+    def addSkip(self, test, reason):
+        self.events.append(('addSkip', self.test_index, reason))
+
+    def addExpectedFailure(self, test, err):
+        self.events.append(('addExpectedFailure', self.test_index, err))
+
+    def addUnexpectedSuccess(self, test):
+        self.events.append(('addUnexpectedSuccess', self.test_index))
+        self.stop_if_failfast()
+
+
+class RemoteTestRunner(object):
+    """
+    Run tests and record everything but don't display anything.
+
+    The implementation matches the unpythonic coding style of unittest2.
+    """
+
+    resultclass = RemoteTestResult
+
+    def __init__(self, failfast=False, resultclass=None):
+        self.failfast = failfast
+        if resultclass is not None:
+            self.resultclass = resultclass
+
+    def run(self, test):
+        result = self.resultclass()
+        unittest.registerResult(result)
+        result.failfast = self.failfast
+        test(result)
+        return result
+
+
+def default_test_processes():
+    """
+    Default number of test processes when using the --parallel option.
+    """
+    try:
+        return int(os.environ['DJANGO_TEST_PROCESSES'])
+    except KeyError:
+        return multiprocessing.cpu_count()
+
+
+def _run_subsuite(args):
+    """
+    Run a suite of tests with a RemoteTestRunner and return a RemoteTestResult.
+
+    This helper lives at module-level and its arguments are wrapped in a tuple
+    because of idiosyncrasies of Python's multiprocessing module.
+    """
+    subsuite_index, subsuite, failfast = args
+    runner = RemoteTestRunner(failfast=failfast)
+    result = runner.run(subsuite)
+    return subsuite_index, result.events
+
+
+class ParallelTestSuite(unittest.TestSuite):
+    """
+    Run a series of tests in parallel in several processes.
+
+    While the unittest module's documentation implies that orchestrating the
+    execution of tests is the responsibility of the test runner, in practice,
+    it appears that TestRunner classes are more concerned with formatting and
+    displaying test results.
+
+    Since there are fewer use cases for customizing TestSuite than TestRunner,
+    implementing parallelization at the level of the TestSuite improves
+    interoperability with existing custom test runners. A single instance of a
+    test runner can still collect results from all tests without being aware
+    that they have been run in parallel.
+    """
+
+    def __init__(self, suite, processes, failfast=False):
+        self.subsuites = partition_suite_by_case(suite)
+        self.processes = processes
+        self.failfast = failfast
+        super(ParallelTestSuite, self).__init__()
+
+    def run(self, result):
+        """
+        Distribute test cases across workers.
+
+        Return an identifier of each test case with its result in order to use
+        imap_unordered to show results as soon as they're available.
+
+        To minimize pickling errors when getting results from workers:
+
+        - pass back numeric indexes in self.subsuites instead of tests
+        - make tracebacks pickleable with tblib, if available
+
+        Even with tblib, errors may still occur for dynamically created
+        exception classes such Model.DoesNotExist which cannot be unpickled.
+        """
+        if tblib is not None:
+            tblib.pickling_support.install()
+
+        pool = multiprocessing.Pool(processes=self.processes)
+        args = [
+            (index, subsuite, self.failfast)
+            for index, subsuite in enumerate(self.subsuites)
+        ]
+        test_results = pool.imap_unordered(_run_subsuite, args)
+
+        while True:
+            if result.shouldStop:
+                pool.terminate()
+                break
+
+            try:
+                subsuite_index, events = test_results.next(timeout=0.1)
+            except multiprocessing.TimeoutError:
+                continue
+            except StopIteration:
+                pool.close()
+                break
+
+            tests = list(self.subsuites[subsuite_index])
+            for event in events:
+                event_name = event[0]
+                handler = getattr(result, event_name, None)
+                if handler is None:
+                    continue
+                test = tests[event[1]]
+                args = event[2:]
+                handler(test, *args)
+
+        pool.join()
+
+        return result
+
+
 class DiscoverRunner(object):
     """
     A Django test runner that uses unittest2 test discovery.
     """
 
-    test_suite = TestSuite
+    test_suite = unittest.TestSuite
     test_runner = unittest.TextTestRunner
-    test_loader = defaultTestLoader
+    test_loader = unittest.defaultTestLoader
     reorder_by = (TestCase, SimpleTestCase)
 
     def __init__(self, pattern=None, top_level=None, verbosity=1,
                  interactive=True, failfast=False, keepdb=False,
-                 reverse=False, debug_sql=False, **kwargs):
+                 reverse=False, debug_sql=False, parallel=0,
+                 **kwargs):
 
         self.pattern = pattern
         self.top_level = top_level
@@ -77,6 +270,7 @@ class DiscoverRunner(object):
         self.keepdb = keepdb
         self.reverse = reverse
         self.debug_sql = debug_sql
+        self.parallel = parallel
 
     @classmethod
     def add_arguments(cls, parser):
@@ -95,6 +289,10 @@ class DiscoverRunner(object):
         parser.add_argument('-d', '--debug-sql', action='store_true', dest='debug_sql',
             default=False,
             help='Prints logged SQL queries on failure.')
+        parser.add_argument(
+            '--parallel', dest='parallel', nargs='?', default=1, type=int,
+            const=default_test_processes(),
+            help='Run tests in parallel processes.')
 
     def setup_test_environment(self, **kwargs):
         setup_test_environment()
@@ -160,7 +358,12 @@ class DiscoverRunner(object):
         for test in extra_tests:
             suite.addTest(test)
 
-        return reorder_suite(suite, self.reorder_by, self.reverse)
+        suite = reorder_suite(suite, self.reorder_by, self.reverse)
+
+        if self.parallel > 1:
+            suite = ParallelTestSuite(suite, self.parallel, self.failfast)
+
+        return suite
 
     def setup_databases(self, **kwargs):
         return setup_databases(
@@ -288,14 +491,14 @@ def reorder_suite(suite, classes, reverse=False):
     class_count = len(classes)
     suite_class = type(suite)
     bins = [OrderedSet() for i in range(class_count + 1)]
-    partition_suite(suite, classes, bins, reverse=reverse)
+    partition_suite_by_type(suite, classes, bins, reverse=reverse)
     reordered_suite = suite_class()
     for i in range(class_count + 1):
         reordered_suite.addTests(bins[i])
     return reordered_suite
 
 
-def partition_suite(suite, classes, bins, reverse=False):
+def partition_suite_by_type(suite, classes, bins, reverse=False):
     """
     Partitions a test suite by test type. Also prevents duplicated tests.
 
@@ -311,7 +514,7 @@ def partition_suite(suite, classes, bins, reverse=False):
         suite = reversed(tuple(suite))
     for test in suite:
         if isinstance(test, suite_class):
-            partition_suite(test, classes, bins, reverse=reverse)
+            partition_suite_by_type(test, classes, bins, reverse=reverse)
         else:
             for i in range(len(classes)):
                 if isinstance(test, classes[i]):
@@ -321,6 +524,21 @@ def partition_suite(suite, classes, bins, reverse=False):
                 bins[-1].add(test)
 
 
+def partition_suite_by_case(suite):
+    """
+    Partitions a test suite by test case, preserving the order of tests.
+    """
+    groups = []
+    suite_class = type(suite)
+    for test_type, test_group in itertools.groupby(suite, type):
+        if issubclass(test_type, unittest.TestCase):
+            groups.append(suite_class(test_group))
+        else:
+            for item in test_group:
+                groups.extend(partition_suite_by_case(item))
+    return groups
+
+
 def get_unique_databases():
     """
     Figure out which databases actually need to be created.
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 35a02eecc8..939ea61731 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1257,6 +1257,26 @@ The ``--debug-sql`` option can be used to enable :ref:`SQL logging
 <django-db-logger>` for failing tests. If :djadminopt:`--verbosity` is ``2``,
 then queries in passing tests are also output.
 
+.. django-admin-option:: --parallel
+
+.. versionadded:: 1.9
+
+The ``--parallel`` option can be used to run tests in parallel in separate
+processes. Since modern processors have multiple cores, this allows running
+tests significantly faster.
+
+By default ``--parallel`` runs one process per core according to
+:func:`multiprocessing.cpu_count()`. You can adjust the number of processes
+either by providing it as the option's value, e.g. ``--parallel=4``, or by
+setting the ``DJANGO_TEST_PROCESSES`` environment variable.
+
+This option requires the third-party ``tblib`` package to display tracebacks
+correctly:
+
+.. code-block:: console
+
+    $ pip install tblib
+
 testserver <fixture fixture ...>
 --------------------------------
 
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index 366e1ac934..ba0402712d 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -125,6 +125,12 @@ degradation.
 
 .. _YUI's A-grade: https://github.com/yui/yui3/wiki/Graded-Browser-Support
 
+Running tests in parallel
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The :djadmin:`test` command now supports a :djadminopt:`--parallel` option to
+run a project's tests in multiple processes in parallel.
+
 Minor features
 ~~~~~~~~~~~~~~
 
diff --git a/tests/runtests.py b/tests/runtests.py
index 97c09c7372..095a9db8df 100755
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -13,6 +13,7 @@ from django.apps import apps
 from django.conf import settings
 from django.db import connection
 from django.test import TestCase, TransactionTestCase
+from django.test.runner import default_test_processes
 from django.test.utils import get_runner
 from django.utils import six
 from django.utils._os import upath
@@ -93,9 +94,10 @@ def get_installed():
     return [app_config.name for app_config in apps.get_app_configs()]
 
 
-def setup(verbosity, test_labels):
+def setup(verbosity, test_labels, parallel):
     if verbosity >= 1:
-        print("Testing against Django installed in '%s'" % os.path.dirname(django.__file__))
+        print("Testing against Django installed in '%s' with %d processes" % (
+            os.path.dirname(django.__file__), parallel))
 
     # Force declaring available_apps in TransactionTestCase for faster tests.
     def no_available_apps(self):
@@ -232,8 +234,9 @@ def teardown(state):
         setattr(settings, key, value)
 
 
-def django_tests(verbosity, interactive, failfast, keepdb, reverse, test_labels, debug_sql):
-    state = setup(verbosity, test_labels)
+def django_tests(verbosity, interactive, failfast, keepdb, reverse,
+                 test_labels, debug_sql, parallel):
+    state = setup(verbosity, test_labels, parallel)
     extra_tests = []
 
     # Run the test suite, including the extra validation tests.
@@ -248,6 +251,7 @@ def django_tests(verbosity, interactive, failfast, keepdb, reverse, test_labels,
         keepdb=keepdb,
         reverse=reverse,
         debug_sql=debug_sql,
+        parallel=parallel,
     )
     failures = test_runner.run_tests(
         test_labels or get_installed(),
@@ -389,10 +393,15 @@ if __name__ == "__main__":
              'is localhost:8081.')
     parser.add_argument(
         '--selenium', action='store_true', dest='selenium', default=False,
-        help='Run the Selenium tests as well (if Selenium is installed)')
+        help='Run the Selenium tests as well (if Selenium is installed).')
     parser.add_argument(
         '--debug-sql', action='store_true', dest='debug_sql', default=False,
-        help='Turn on the SQL query logger within tests')
+        help='Turn on the SQL query logger within tests.')
+    parser.add_argument(
+        '--parallel', dest='parallel', nargs='?', default=1, type=int,
+        const=default_test_processes(),
+        help='Run tests in parallel processes.')
+
     options = parser.parse_args()
 
     # mock is a required dependency
@@ -429,6 +438,6 @@ if __name__ == "__main__":
         failures = django_tests(options.verbosity, options.interactive,
                                 options.failfast, options.keepdb,
                                 options.reverse, options.modules,
-                                options.debug_sql)
+                                options.debug_sql, options.parallel)
         if failures:
             sys.exit(bool(failures))

From 0586c061f0b857e2259bea48e21ebb69a7878d13 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Mon, 9 Feb 2015 22:00:09 +0100
Subject: [PATCH 02/17] Cloned databases for running tests in parallel.

---
 django/db/backends/base/creation.py       | 52 ++++++++++++++++++++--
 django/db/backends/mysql/creation.py      | 36 +++++++++++++++
 django/db/backends/postgresql/creation.py | 28 ++++++++++++
 django/db/backends/sqlite3/creation.py    | 34 +++++++++++++++
 django/test/runner.py                     | 53 ++++++++++++++++++++---
 docs/ref/django-admin.txt                 |  4 ++
 docs/releases/1.9.txt                     |  8 ++++
 tests/test_runner/tests.py                |  4 +-
 8 files changed, 208 insertions(+), 11 deletions(-)

diff --git a/django/db/backends/base/creation.py b/django/db/backends/base/creation.py
index 82ccadcbe7..888dc792fe 100644
--- a/django/db/backends/base/creation.py
+++ b/django/db/backends/base/creation.py
@@ -190,13 +190,56 @@ class BaseDatabaseCreation(object):
 
         return test_database_name
 
-    def destroy_test_db(self, old_database_name, verbosity=1, keepdb=False):
+    def clone_test_db(self, number, verbosity=1, autoclobber=False, keepdb=False):
+        """
+        Clone a test database.
+        """
+        source_database_name = self.connection.settings_dict['NAME']
+
+        if verbosity >= 1:
+            test_db_repr = ''
+            action = 'Cloning test database'
+            if verbosity >= 2:
+                test_db_repr = " ('%s')" % source_database_name
+            if keepdb:
+                action = 'Using existing clone'
+            print("%s for alias '%s'%s..." % (action, self.connection.alias, test_db_repr))
+
+        # We could skip this call if keepdb is True, but we instead
+        # give it the keepdb param. See create_test_db for details.
+        self._clone_test_db(number, verbosity, keepdb)
+
+    def get_test_db_clone_settings(self, number):
+        """
+        Return a modified connection settings dict for the n-th clone of a DB.
+        """
+        # When this function is called, the test database has been created
+        # already and its name has been copied to settings_dict['NAME'] so
+        # we don't need to call _get_test_db_name.
+        orig_settings_dict = self.connection.settings_dict
+        new_settings_dict = orig_settings_dict.copy()
+        new_settings_dict['NAME'] = '{}_{}'.format(orig_settings_dict['NAME'], number)
+        return new_settings_dict
+
+    def _clone_test_db(self, number, verbosity, keepdb=False):
+        """
+        Internal implementation - duplicate the test db tables.
+        """
+        raise NotImplementedError(
+            "The database backend doesn't support cloning databases. "
+            "Disable the option to run tests in parallel processes.")
+
+    def destroy_test_db(self, old_database_name=None, verbosity=1, keepdb=False, number=None):
         """
         Destroy a test database, prompting the user for confirmation if the
         database already exists.
         """
         self.connection.close()
-        test_database_name = self.connection.settings_dict['NAME']
+        if number is None:
+            test_database_name = self.connection.settings_dict['NAME']
+        else:
+            test_database_name = self.get_test_db_clone_settings(number)['NAME']
+
         if verbosity >= 1:
             test_db_repr = ''
             action = 'Destroying'
@@ -213,8 +256,9 @@ class BaseDatabaseCreation(object):
             self._destroy_test_db(test_database_name, verbosity)
 
         # Restore the original database name
-        settings.DATABASES[self.connection.alias]["NAME"] = old_database_name
-        self.connection.settings_dict["NAME"] = old_database_name
+        if old_database_name is not None:
+            settings.DATABASES[self.connection.alias]["NAME"] = old_database_name
+            self.connection.settings_dict["NAME"] = old_database_name
 
     def _destroy_test_db(self, test_database_name, verbosity):
         """
diff --git a/django/db/backends/mysql/creation.py b/django/db/backends/mysql/creation.py
index aba9e8b841..a992e65952 100644
--- a/django/db/backends/mysql/creation.py
+++ b/django/db/backends/mysql/creation.py
@@ -1,5 +1,10 @@
+import subprocess
+import sys
+
 from django.db.backends.base.creation import BaseDatabaseCreation
 
+from .client import DatabaseClient
+
 
 class DatabaseCreation(BaseDatabaseCreation):
 
@@ -11,3 +16,34 @@ class DatabaseCreation(BaseDatabaseCreation):
         if test_settings['COLLATION']:
             suffix.append('COLLATE %s' % test_settings['COLLATION'])
         return ' '.join(suffix)
+
+    def _clone_test_db(self, number, verbosity, keepdb=False):
+        qn = self.connection.ops.quote_name
+        source_database_name = self.connection.settings_dict['NAME']
+        target_database_name = self.get_test_db_clone_settings(number)['NAME']
+
+        with self._nodb_connection.cursor() as cursor:
+            try:
+                cursor.execute("CREATE DATABASE %s" % qn(target_database_name))
+            except Exception as e:
+                if keepdb:
+                    return
+                try:
+                    if verbosity >= 1:
+                        print("Destroying old test database '%s'..." % self.connection.alias)
+                    cursor.execute("DROP DATABASE %s" % qn(target_database_name))
+                    cursor.execute("CREATE DATABASE %s" % qn(target_database_name))
+                except Exception as e:
+                    sys.stderr.write("Got an error recreating the test database: %s\n" % e)
+                    sys.exit(2)
+
+        dump_cmd = DatabaseClient.settings_to_cmd_args(self.connection.settings_dict)
+        dump_cmd[0] = 'mysqldump'
+        dump_cmd[-1] = source_database_name
+        load_cmd = DatabaseClient.settings_to_cmd_args(self.connection.settings_dict)
+        load_cmd[-1] = target_database_name
+
+        dump_proc = subprocess.Popen(dump_cmd, stdout=subprocess.PIPE)
+        load_proc = subprocess.Popen(load_cmd, stdin=dump_proc.stdout, stdout=subprocess.PIPE)
+        dump_proc.stdout.close()    # allow dump_proc to receive a SIGPIPE if load_proc exits.
+        load_proc.communicate()
diff --git a/django/db/backends/postgresql/creation.py b/django/db/backends/postgresql/creation.py
index 13eea0d3b7..dcb0430f1b 100644
--- a/django/db/backends/postgresql/creation.py
+++ b/django/db/backends/postgresql/creation.py
@@ -1,3 +1,5 @@
+import sys
+
 from django.db.backends.base.creation import BaseDatabaseCreation
 
 
@@ -11,3 +13,29 @@ class DatabaseCreation(BaseDatabaseCreation):
         if test_settings['CHARSET']:
             return "WITH ENCODING '%s'" % test_settings['CHARSET']
         return ''
+
+    def _clone_test_db(self, number, verbosity, keepdb=False):
+        # CREATE DATABASE ... WITH TEMPLATE ... requires closing connections
+        # to the template database.
+        self.connection.close()
+
+        qn = self.connection.ops.quote_name
+        source_database_name = self.connection.settings_dict['NAME']
+        target_database_name = self.get_test_db_clone_settings(number)['NAME']
+
+        with self._nodb_connection.cursor() as cursor:
+            try:
+                cursor.execute("CREATE DATABASE %s WITH TEMPLATE %s" % (
+                    qn(target_database_name), qn(source_database_name)))
+            except Exception as e:
+                if keepdb:
+                    return
+                try:
+                    if verbosity >= 1:
+                        print("Destroying old test database '%s'..." % self.connection.alias)
+                    cursor.execute("DROP DATABASE %s" % qn(target_database_name))
+                    cursor.execute("CREATE DATABASE %s WITH TEMPLATE %s" % (
+                        qn(target_database_name), qn(source_database_name)))
+                except Exception as e:
+                    sys.stderr.write("Got an error cloning the test database: %s\n" % e)
+                    sys.exit(2)
diff --git a/django/db/backends/sqlite3/creation.py b/django/db/backends/sqlite3/creation.py
index d8fde0c9b7..d52349e57f 100644
--- a/django/db/backends/sqlite3/creation.py
+++ b/django/db/backends/sqlite3/creation.py
@@ -1,4 +1,5 @@
 import os
+import shutil
 import sys
 
 from django.core.exceptions import ImproperlyConfigured
@@ -47,6 +48,39 @@ class DatabaseCreation(BaseDatabaseCreation):
                     sys.exit(1)
         return test_database_name
 
+    def get_test_db_clone_settings(self, number):
+        orig_settings_dict = self.connection.settings_dict
+        source_database_name = orig_settings_dict['NAME']
+        if self.connection.is_in_memory_db(source_database_name):
+            return orig_settings_dict
+        else:
+            new_settings_dict = orig_settings_dict.copy()
+            root, ext = os.path.splitext(orig_settings_dict['NAME'])
+            new_settings_dict['NAME'] = '{}_{}.{}'.format(root, number, ext)
+            return new_settings_dict
+
+    def _clone_test_db(self, number, verbosity, keepdb=False):
+        source_database_name = self.connection.settings_dict['NAME']
+        target_database_name = self.get_test_db_clone_settings(number)['NAME']
+        # Forking automatically makes a copy of an in-memory database.
+        if not self.connection.is_in_memory_db(source_database_name):
+            # Erase the old test database
+            if os.access(target_database_name, os.F_OK):
+                if keepdb:
+                    return
+                if verbosity >= 1:
+                    print("Destroying old test database '%s'..." % target_database_name)
+                try:
+                    os.remove(target_database_name)
+                except Exception as e:
+                    sys.stderr.write("Got an error deleting the old test database: %s\n" % e)
+                    sys.exit(2)
+            try:
+                shutil.copy(source_database_name, target_database_name)
+            except Exception as e:
+                sys.stderr.write("Got an error cloning the test database: %s\n" % e)
+                sys.exit(2)
+
     def _destroy_test_db(self, test_database_name, verbosity):
         if test_database_name and not self.connection.is_in_memory_db(test_database_name):
             # Remove the SQLite database file
diff --git a/django/test/runner.py b/django/test/runner.py
index 0ed21fc1c8..cd12d6203f 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -1,4 +1,5 @@
 import collections
+import ctypes
 import itertools
 import logging
 import multiprocessing
@@ -158,12 +159,36 @@ def default_test_processes():
         return multiprocessing.cpu_count()
 
 
+_worker_id = 0
+
+
+def _init_worker(counter):
+    """
+    Switch to databases dedicated to this worker.
+
+    This helper lives at module-level because of the multiprocessing module's
+    requirements.
+    """
+
+    global _worker_id
+
+    with counter.get_lock():
+        counter.value += 1
+        _worker_id = counter.value
+
+    for alias in connections:
+        connection = connections[alias]
+        settings_dict = connection.creation.get_test_db_clone_settings(_worker_id)
+        connection.settings_dict = settings_dict
+        connection.close()
+
+
 def _run_subsuite(args):
     """
     Run a suite of tests with a RemoteTestRunner and return a RemoteTestResult.
 
     This helper lives at module-level and its arguments are wrapped in a tuple
-    because of idiosyncrasies of Python's multiprocessing module.
+    because of the multiprocessing module's requirements.
     """
     subsuite_index, subsuite, failfast = args
     runner = RemoteTestRunner(failfast=failfast)
@@ -211,7 +236,11 @@ class ParallelTestSuite(unittest.TestSuite):
         if tblib is not None:
             tblib.pickling_support.install()
 
-        pool = multiprocessing.Pool(processes=self.processes)
+        counter = multiprocessing.Value(ctypes.c_int, 0)
+        pool = multiprocessing.Pool(
+            processes=self.processes,
+            initializer=_init_worker,
+            initargs=[counter])
         args = [
             (index, subsuite, self.failfast)
             for index, subsuite in enumerate(self.subsuites)
@@ -368,7 +397,7 @@ class DiscoverRunner(object):
     def setup_databases(self, **kwargs):
         return setup_databases(
             self.verbosity, self.interactive, self.keepdb, self.debug_sql,
-            **kwargs
+            self.parallel, **kwargs
         )
 
     def get_resultclass(self):
@@ -388,6 +417,13 @@ class DiscoverRunner(object):
         """
         for connection, old_name, destroy in old_config:
             if destroy:
+                if self.parallel > 1:
+                    for index in range(self.parallel):
+                        connection.creation.destroy_test_db(
+                            number=index + 1,
+                            verbosity=self.verbosity,
+                            keepdb=self.keepdb,
+                        )
                 connection.creation.destroy_test_db(old_name, self.verbosity, self.keepdb)
 
     def teardown_test_environment(self, **kwargs):
@@ -581,7 +617,7 @@ def get_unique_databases():
     return test_databases
 
 
-def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, **kwargs):
+def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, parallel=0, **kwargs):
     """
     Creates the test databases.
     """
@@ -599,11 +635,18 @@ def setup_databases(verbosity, interactive, keepdb=False, debug_sql=False, **kwa
             if first_alias is None:
                 first_alias = alias
                 connection.creation.create_test_db(
-                    verbosity,
+                    verbosity=verbosity,
                     autoclobber=not interactive,
                     keepdb=keepdb,
                     serialize=connection.settings_dict.get("TEST", {}).get("SERIALIZE", True),
                 )
+                if parallel > 1:
+                    for index in range(parallel):
+                        connection.creation.clone_test_db(
+                            number=index + 1,
+                            verbosity=verbosity,
+                            keepdb=keepdb,
+                        )
             # Configure all other connections as mirrors of the first one
             else:
                 connections[alias].creation.set_as_test_mirror(
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 939ea61731..3dd4cf3a6d 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1270,6 +1270,10 @@ By default ``--parallel`` runs one process per core according to
 either by providing it as the option's value, e.g. ``--parallel=4``, or by
 setting the ``DJANGO_TEST_PROCESSES`` environment variable.
 
+Each process gets its own database. You must ensure that different test cases
+don't access the same resources. For instance, test cases that touch the
+filesystem should create a temporary directory for their own use.
+
 This option requires the third-party ``tblib`` package to display tracebacks
 correctly:
 
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index ba0402712d..f1d59fce16 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -131,6 +131,10 @@ Running tests in parallel
 The :djadmin:`test` command now supports a :djadminopt:`--parallel` option to
 run a project's tests in multiple processes in parallel.
 
+Each process gets its own database. You must ensure that different test cases
+don't access the same resources. For instance, test cases that touch the
+filesystem should create a temporary directory for their own use.
+
 Minor features
 ~~~~~~~~~~~~~~
 
@@ -681,6 +685,10 @@ Database backend API
   before 1.0, but hasn't been overridden by any core backend in years
   and hasn't been called anywhere in Django's code or tests.
 
+* In order to support test parallelization, you must implement the
+  ``DatabaseCreation._clone_test_db()`` method. You may have to adjust
+  ``DatabaseCreation.get_test_db_clone_settings()``.
+
 Default settings that were tuples are now lists
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index 8e9991d654..bf0b8795cc 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -319,7 +319,7 @@ class SetupDatabasesTests(unittest.TestCase):
             with mock.patch('django.test.runner.connections', new=tested_connections):
                 self.runner_instance.setup_databases()
         mocked_db_creation.return_value.create_test_db.assert_called_once_with(
-            0, autoclobber=False, serialize=True, keepdb=False
+            verbosity=0, autoclobber=False, serialize=True, keepdb=False
         )
 
     def test_serialized_off(self):
@@ -333,7 +333,7 @@ class SetupDatabasesTests(unittest.TestCase):
             with mock.patch('django.test.runner.connections', new=tested_connections):
                 self.runner_instance.setup_databases()
         mocked_db_creation.return_value.create_test_db.assert_called_once_with(
-            0, autoclobber=False, serialize=False, keepdb=False
+            verbosity=0, autoclobber=False, serialize=False, keepdb=False
         )
 
 

From d6be404e565fd04538ebc4771aa98422cc03fd2e Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 4 Jun 2015 18:35:18 +0200
Subject: [PATCH 03/17] Changed strategy for removing TMPDIR in runtests.py.

Previously, a traceback would be displayed on exit because:
- using some multiprocessing features creates a temporary directory
- this directory would be inside TMPDIR
- multiprocessing would attempt to remove it when a particular object
  was deallocated, after runtests.py had already removed it along with
  everything else in TMPDIR.
---
 tests/runtests.py | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/tests/runtests.py b/tests/runtests.py
index 095a9db8df..58181a0e92 100755
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+import atexit
 import logging
 import os
 import shutil
@@ -35,6 +36,12 @@ TMPDIR = tempfile.mkdtemp(prefix='django_')
 # so that children processes inherit it.
 tempfile.tempdir = os.environ['TMPDIR'] = TMPDIR
 
+# Removing the temporary TMPDIR. Ensure we pass in unicode so that it will
+# successfully remove temp trees containing non-ASCII filenames on Windows.
+# (We're assuming the temp dir name itself only contains ASCII characters.)
+atexit.register(shutil.rmtree, six.text_type(TMPDIR))
+
+
 SUBDIRS_TO_SKIP = [
     'data',
     'import_error_package',
@@ -220,15 +227,6 @@ def setup(verbosity, test_labels, parallel):
 
 
 def teardown(state):
-    try:
-        # Removing the temporary TMPDIR. Ensure we pass in unicode
-        # so that it will successfully remove temp trees containing
-        # non-ASCII filenames on Windows. (We're assuming the temp dir
-        # name itself does not contain non-ASCII characters.)
-        shutil.rmtree(six.text_type(TMPDIR))
-    except OSError:
-        print('Failed to remove temp directory: %s' % TMPDIR)
-
     # Restore the old settings.
     for key, value in state.items():
         setattr(settings, key, value)

From 442baabd0bd1453a71eaa51d43f636bb6ad56b6f Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 5 Feb 2015 21:29:11 +0100
Subject: [PATCH 04/17] Supported running admin_script testcases concurrently.

---
 tests/admin_scripts/tests.py | 73 ++++++++++++++++++++++--------------
 1 file changed, 44 insertions(+), 29 deletions(-)

diff --git a/tests/admin_scripts/tests.py b/tests/admin_scripts/tests.py
index 616082346b..397856912e 100644
--- a/tests/admin_scripts/tests.py
+++ b/tests/admin_scripts/tests.py
@@ -33,23 +33,38 @@ from django.utils._os import npath, upath
 from django.utils.encoding import force_text
 from django.utils.six import PY3, StringIO
 
-test_dir = os.path.realpath(os.path.join(tempfile.gettempdir(), 'test_project'))
-if not os.path.exists(test_dir):
-    os.mkdir(test_dir)
-    open(os.path.join(test_dir, '__init__.py'), 'w').close()
-
 custom_templates_dir = os.path.join(os.path.dirname(upath(__file__)), 'custom_templates')
+
 SYSTEM_CHECK_MSG = 'System check identified no issues'
 
 
 class AdminScriptTestCase(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        super(AdminScriptTestCase, cls).setUpClass()
+        cls.test_dir = os.path.realpath(os.path.join(
+            tempfile.gettempdir(),
+            cls.__name__,
+            'test_project',
+        ))
+        if not os.path.exists(cls.test_dir):
+            os.makedirs(cls.test_dir)
+        with open(os.path.join(cls.test_dir, '__init__.py'), 'w'):
+            pass
+
+    @classmethod
+    def tearDownClass(cls):
+        shutil.rmtree(cls.test_dir)
+        super(AdminScriptTestCase, cls).tearDownClass()
+
     def write_settings(self, filename, apps=None, is_dir=False, sdict=None, extra=None):
         if is_dir:
-            settings_dir = os.path.join(test_dir, filename)
+            settings_dir = os.path.join(self.test_dir, filename)
             os.mkdir(settings_dir)
             settings_file_path = os.path.join(settings_dir, '__init__.py')
         else:
-            settings_file_path = os.path.join(test_dir, filename)
+            settings_file_path = os.path.join(self.test_dir, filename)
 
         with open(settings_file_path, 'w') as settings_file:
             settings_file.write('# -*- coding: utf-8 -*\n')
@@ -78,7 +93,7 @@ class AdminScriptTestCase(unittest.TestCase):
                     settings_file.write("%s = %s\n" % (k, v))
 
     def remove_settings(self, filename, is_dir=False):
-        full_name = os.path.join(test_dir, filename)
+        full_name = os.path.join(self.test_dir, filename)
         if is_dir:
             shutil.rmtree(full_name)
         else:
@@ -96,7 +111,7 @@ class AdminScriptTestCase(unittest.TestCase):
         except OSError:
             pass
         # Also remove a __pycache__ directory, if it exists
-        cache_name = os.path.join(test_dir, '__pycache__')
+        cache_name = os.path.join(self.test_dir, '__pycache__')
         if os.path.isdir(cache_name):
             shutil.rmtree(cache_name)
 
@@ -115,7 +130,7 @@ class AdminScriptTestCase(unittest.TestCase):
         return paths
 
     def run_test(self, script, args, settings_file=None, apps=None):
-        base_dir = os.path.dirname(test_dir)
+        base_dir = os.path.dirname(self.test_dir)
         # The base dir for Django's tests is one level up.
         tests_dir = os.path.dirname(os.path.dirname(upath(__file__)))
         # The base dir for Django is one level above the test dir. We don't use
@@ -145,7 +160,7 @@ class AdminScriptTestCase(unittest.TestCase):
         test_environ[str('PYTHONWARNINGS')] = str('')
 
         # Move to the test directory and run
-        os.chdir(test_dir)
+        os.chdir(self.test_dir)
         out, err = subprocess.Popen([sys.executable, script] + args,
                 stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                 env=test_environ, universal_newlines=True).communicate()
@@ -168,7 +183,7 @@ class AdminScriptTestCase(unittest.TestCase):
         conf_dir = os.path.dirname(upath(conf.__file__))
         template_manage_py = os.path.join(conf_dir, 'project_template', 'manage.py')
 
-        test_manage_py = os.path.join(test_dir, 'manage.py')
+        test_manage_py = os.path.join(self.test_dir, 'manage.py')
         shutil.copyfile(template_manage_py, test_manage_py)
 
         with open(test_manage_py, 'r') as fp:
@@ -590,7 +605,7 @@ class DjangoAdminSettingsDirectory(AdminScriptTestCase):
     def test_setup_environ(self):
         "directory: startapp creates the correct directory"
         args = ['startapp', 'settings_test']
-        app_path = os.path.join(test_dir, 'settings_test')
+        app_path = os.path.join(self.test_dir, 'settings_test')
         out, err = self.run_django_admin(args, 'test_project.settings')
         self.addCleanup(shutil.rmtree, app_path)
         self.assertNoOutput(err)
@@ -611,7 +626,7 @@ class DjangoAdminSettingsDirectory(AdminScriptTestCase):
         "directory: startapp creates the correct directory with a custom template"
         template_path = os.path.join(custom_templates_dir, 'app_template')
         args = ['startapp', '--template', template_path, 'custom_settings_test']
-        app_path = os.path.join(test_dir, 'custom_settings_test')
+        app_path = os.path.join(self.test_dir, 'custom_settings_test')
         out, err = self.run_django_admin(args, 'test_project.settings')
         self.addCleanup(shutil.rmtree, app_path)
         self.assertNoOutput(err)
@@ -1047,7 +1062,7 @@ class ManageSettingsWithSettingsErrors(AdminScriptTestCase):
         self.remove_settings('settings.py')
 
     def write_settings_with_import_error(self, filename):
-        settings_file_path = os.path.join(test_dir, filename)
+        settings_file_path = os.path.join(self.test_dir, filename)
         with open(settings_file_path, 'w') as settings_file:
             settings_file.write('# Settings file automatically generated by admin_scripts test case\n')
             settings_file.write('# The next line will cause an import error:\nimport foo42bar\n')
@@ -1802,7 +1817,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
     def test_simple_project(self):
         "Make sure the startproject management command creates a project"
         args = ['startproject', 'testproject']
-        testproject_dir = os.path.join(test_dir, 'testproject')
+        testproject_dir = os.path.join(self.test_dir, 'testproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1818,7 +1833,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Make sure the startproject management command validates a project name"
         for bad_name in ('7testproject', '../testproject'):
             args = ['startproject', bad_name]
-            testproject_dir = os.path.join(test_dir, bad_name)
+            testproject_dir = os.path.join(self.test_dir, bad_name)
             self.addCleanup(shutil.rmtree, testproject_dir, True)
 
             out, err = self.run_django_admin(args)
@@ -1829,7 +1844,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
     def test_simple_project_different_directory(self):
         "Make sure the startproject management command creates a project in a specific directory"
         args = ['startproject', 'testproject', 'othertestproject']
-        testproject_dir = os.path.join(test_dir, 'othertestproject')
+        testproject_dir = os.path.join(self.test_dir, 'othertestproject')
         os.mkdir(testproject_dir)
         self.addCleanup(shutil.rmtree, testproject_dir)
 
@@ -1846,7 +1861,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Make sure the startproject management command is able to use a different project template"
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['startproject', '--template', template_path, 'customtestproject']
-        testproject_dir = os.path.join(test_dir, 'customtestproject')
+        testproject_dir = os.path.join(self.test_dir, 'customtestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1858,7 +1873,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Ticket 17475: Template dir passed has a trailing path separator"
         template_path = os.path.join(custom_templates_dir, 'project_template' + os.sep)
         args = ['startproject', '--template', template_path, 'customtestproject']
-        testproject_dir = os.path.join(test_dir, 'customtestproject')
+        testproject_dir = os.path.join(self.test_dir, 'customtestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1870,7 +1885,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Make sure the startproject management command is able to use a different project template from a tarball"
         template_path = os.path.join(custom_templates_dir, 'project_template.tgz')
         args = ['startproject', '--template', template_path, 'tarballtestproject']
-        testproject_dir = os.path.join(test_dir, 'tarballtestproject')
+        testproject_dir = os.path.join(self.test_dir, 'tarballtestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1882,7 +1897,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Startproject can use a project template from a tarball and create it in a specified location"
         template_path = os.path.join(custom_templates_dir, 'project_template.tgz')
         args = ['startproject', '--template', template_path, 'tarballtestproject', 'altlocation']
-        testproject_dir = os.path.join(test_dir, 'altlocation')
+        testproject_dir = os.path.join(self.test_dir, 'altlocation')
         os.mkdir(testproject_dir)
         self.addCleanup(shutil.rmtree, testproject_dir)
 
@@ -1896,7 +1911,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         template_url = '%s/custom_templates/project_template.tgz' % self.live_server_url
 
         args = ['startproject', '--template', template_url, 'urltestproject']
-        testproject_dir = os.path.join(test_dir, 'urltestproject')
+        testproject_dir = os.path.join(self.test_dir, 'urltestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1909,7 +1924,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         template_url = '%s/custom_templates/project_template.tgz/' % self.live_server_url
 
         args = ['startproject', '--template', template_url, 'urltestproject']
-        testproject_dir = os.path.join(test_dir, 'urltestproject')
+        testproject_dir = os.path.join(self.test_dir, 'urltestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1921,7 +1936,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Make sure the startproject management command is able to render custom files"
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['startproject', '--template', template_path, 'customtestproject', '-e', 'txt', '-n', 'Procfile']
-        testproject_dir = os.path.join(test_dir, 'customtestproject')
+        testproject_dir = os.path.join(self.test_dir, 'customtestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)
@@ -1939,7 +1954,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Make sure template context variables are rendered with proper values"
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['startproject', '--template', template_path, 'another_project', 'project_dir']
-        testproject_dir = os.path.join(test_dir, 'project_dir')
+        testproject_dir = os.path.join(self.test_dir, 'project_dir')
         os.mkdir(testproject_dir)
         self.addCleanup(shutil.rmtree, testproject_dir)
         out, err = self.run_django_admin(args)
@@ -1957,7 +1972,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         self.addCleanup(self.remove_settings, 'alternate_settings.py')
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['custom_startproject', '--template', template_path, 'another_project', 'project_dir', '--extra', '<&>', '--settings=alternate_settings']
-        testproject_dir = os.path.join(test_dir, 'project_dir')
+        testproject_dir = os.path.join(self.test_dir, 'project_dir')
         os.mkdir(testproject_dir)
         self.addCleanup(shutil.rmtree, testproject_dir)
         out, err = self.run_manage(args)
@@ -1974,7 +1989,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         """
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['startproject', '--template', template_path, 'yet_another_project', 'project_dir2']
-        testproject_dir = os.path.join(test_dir, 'project_dir2')
+        testproject_dir = os.path.join(self.test_dir, 'project_dir2')
         out, err = self.run_django_admin(args)
         self.assertNoOutput(out)
         self.assertOutput(err, "Destination directory '%s' does not exist, please create it first." % testproject_dir)
@@ -1984,7 +1999,7 @@ class StartProject(LiveServerTestCase, AdminScriptTestCase):
         "Ticket 18091: Make sure the startproject management command is able to render templates with non-ASCII content"
         template_path = os.path.join(custom_templates_dir, 'project_template')
         args = ['startproject', '--template', template_path, '--extension=txt', 'customtestproject']
-        testproject_dir = os.path.join(test_dir, 'customtestproject')
+        testproject_dir = os.path.join(self.test_dir, 'customtestproject')
         self.addCleanup(shutil.rmtree, testproject_dir, True)
 
         out, err = self.run_django_admin(args)

From e39dd618085bd437bcd800b5a0a7e29751ab6274 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Fri, 5 Jun 2015 13:49:32 +0200
Subject: [PATCH 05/17] Adjusted tests that were messing with database
 connections too heavily.

The previous implementation would result in tests hitting the wrong
database when running tests in parallel on multiple databases.
---
 tests/timezones/tests.py | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/tests/timezones/tests.py b/tests/timezones/tests.py
index 18539687a8..65a052f2cb 100644
--- a/tests/timezones/tests.py
+++ b/tests/timezones/tests.py
@@ -4,6 +4,7 @@ import datetime
 import re
 import sys
 import warnings
+from contextlib import contextmanager
 from unittest import SkipTest, skipIf
 from xml.dom.minidom import parseString
 
@@ -611,27 +612,41 @@ class ForcedTimeZoneDatabaseTests(TransactionTestCase):
             raise SkipTest("Database doesn't support feature(s): test_db_allows_multiple_connections")
 
         super(ForcedTimeZoneDatabaseTests, cls).setUpClass()
-        connections.databases['tz'] = connections.databases['default'].copy()
-        connections.databases['tz']['TIME_ZONE'] = 'Asia/Bangkok'
 
-    @classmethod
-    def tearDownClass(cls):
-        connections['tz'].close()
-        del connections['tz']
-        del connections.databases['tz']
-        super(ForcedTimeZoneDatabaseTests, cls).tearDownClass()
+    @contextmanager
+    def override_database_connection_timezone(self, timezone):
+        try:
+            orig_timezone = connection.settings_dict['TIME_ZONE']
+            connection.settings_dict['TIME_ZONE'] = timezone
+            # Clear cached properties, after first accessing them to ensure they exist.
+            connection.timezone
+            del connection.timezone
+            connection.timezone_name
+            del connection.timezone_name
+
+            yield
+
+        finally:
+            connection.settings_dict['TIME_ZONE'] = orig_timezone
+            # Clear cached properties, after first accessing them to ensure they exist.
+            connection.timezone
+            del connection.timezone
+            connection.timezone_name
+            del connection.timezone_name
 
     def test_read_datetime(self):
         fake_dt = datetime.datetime(2011, 9, 1, 17, 20, 30, tzinfo=UTC)
         Event.objects.create(dt=fake_dt)
 
-        event = Event.objects.using('tz').get()
-        dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
+        with self.override_database_connection_timezone('Asia/Bangkok'):
+            event = Event.objects.get()
+            dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
         self.assertEqual(event.dt, dt)
 
     def test_write_datetime(self):
         dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
-        Event.objects.using('tz').create(dt=dt)
+        with self.override_database_connection_timezone('Asia/Bangkok'):
+            Event.objects.create(dt=dt)
 
         event = Event.objects.get()
         fake_dt = datetime.datetime(2011, 9, 1, 17, 20, 30, tzinfo=UTC)

From 326bc0955b2e9ab6b6cfd62263c9b3fe2fb1d333 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 5 Feb 2015 23:02:10 +0100
Subject: [PATCH 06/17] Allowed a port range for the liveserver by default.

This is required for running tests in parallel.
---
 django/core/management/commands/test.py |  2 +-
 django/test/testcases.py                |  2 +-
 docs/ref/django-admin.txt               |  6 +++++-
 docs/releases/1.9.txt                   |  3 +++
 docs/topics/testing/tools.txt           | 17 ++++++++++++-----
 tests/runtests.py                       |  2 +-
 6 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/django/core/management/commands/test.py b/django/core/management/commands/test.py
index 0d084e1e91..ad54994d74 100644
--- a/django/core/management/commands/test.py
+++ b/django/core/management/commands/test.py
@@ -47,7 +47,7 @@ class Command(BaseCommand):
             action='store', dest='liveserver', default=None,
             help='Overrides the default address where the live server (used '
                  'with LiveServerTestCase) is expected to run from. The '
-                 'default value is localhost:8081.'),
+                 'default value is localhost:8081-8179.'),
 
         test_runner_class = get_runner(settings, self.test_runner)
         if hasattr(test_runner_class, 'option_list'):
diff --git a/django/test/testcases.py b/django/test/testcases.py
index 0c704ad951..fd93ba5bad 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -1318,7 +1318,7 @@ class LiveServerTestCase(TransactionTestCase):
 
         # Launch the live server's thread
         specified_address = os.environ.get(
-            'DJANGO_LIVE_TEST_SERVER_ADDRESS', 'localhost:8081')
+            'DJANGO_LIVE_TEST_SERVER_ADDRESS', 'localhost:8081-8179')
 
         # The specified ports may be of the form '8000-8010,8080,9200-9300'
         # i.e. a comma-separated list of ports or ranges of ports, so we break
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 3dd4cf3a6d..a98b60b45f 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1227,7 +1227,11 @@ provided by the :setting:`TEST_RUNNER` setting.
 
 The ``--liveserver`` option can be used to override the default address where
 the live server (used with :class:`~django.test.LiveServerTestCase`) is
-expected to run from. The default value is ``localhost:8081``.
+expected to run from. The default value is ``localhost:8081-8179``.
+
+.. versionchanged:: 1.9
+
+    In earlier versions, the default value was ``localhost:8081``.
 
 .. django-admin-option:: --keepdb
 
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index f1d59fce16..99b6e44bc3 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -1055,6 +1055,9 @@ Miscellaneous
   changed. They used to be ``(old_names, mirrors)`` tuples. Now they're just
   the first item, ``old_names``.
 
+* By default :class:`~django.test.LiveServerTestCase` attempts to find an
+  available port in the 8081-8179 range instead of just trying port 8081.
+
 .. _deprecated-features-1.9:
 
 Features deprecated in 1.9
diff --git a/docs/topics/testing/tools.txt b/docs/topics/testing/tools.txt
index 28a4921198..52a00b7ded 100644
--- a/docs/topics/testing/tools.txt
+++ b/docs/topics/testing/tools.txt
@@ -812,11 +812,18 @@ This allows the use of automated test clients other than the
 client, to execute a series of functional tests inside a browser and simulate a
 real user's actions.
 
-By default the live server's address is ``'localhost:8081'`` and the full URL
-can be accessed during the tests with ``self.live_server_url``. If you'd like
-to change the default address (in the case, for example, where the 8081 port is
-already taken) then you may pass a different one to the :djadmin:`test` command
-via the :djadminopt:`--liveserver` option, for example:
+By default the live server listens on ``localhost`` and picks the first
+available port in the ``8081-8179`` range. Its full URL can be accessed with
+``self.live_server_url`` during the tests.
+
+.. versionchanged:: 1.9
+
+    In earlier versions, the live server's default address was always
+    ``'localhost:8081'``.
+
+If you'd like to select another address then you may pass a different one to
+the :djadmin:`test` command via the :djadminopt:`--liveserver` option, for
+example:
 
 .. code-block:: console
 
diff --git a/tests/runtests.py b/tests/runtests.py
index 58181a0e92..0577737a5f 100755
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -388,7 +388,7 @@ if __name__ == "__main__":
     parser.add_argument('--liveserver',
         help='Overrides the default address where the live server (used with '
              'LiveServerTestCase) is expected to run from. The default value '
-             'is localhost:8081.')
+             'is localhost:8081-8179.')
     parser.add_argument(
         '--selenium', action='store_true', dest='selenium', default=False,
         help='Run the Selenium tests as well (if Selenium is installed).')

From bf2c969eb7d941812993d69bcf7c8ac35bdb7726 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Fri, 5 Jun 2015 00:02:32 +0200
Subject: [PATCH 07/17] Prevented staticfiles test from colliding when run in
 parallel.

This requires that each test never alters files in static directories
collected by other tests. The alternative is to add a temporary
directory to STATICFILES_DIRS or a new app to INSTALLED_APPS.
---
 tests/staticfiles_tests/settings.py        |  2 -
 tests/staticfiles_tests/test_management.py | 81 +++++++++++-----------
 tests/staticfiles_tests/test_storage.py    | 18 ++++-
 3 files changed, 56 insertions(+), 45 deletions(-)

diff --git a/tests/staticfiles_tests/settings.py b/tests/staticfiles_tests/settings.py
index 1978d6529d..ea20a84c6f 100644
--- a/tests/staticfiles_tests/settings.py
+++ b/tests/staticfiles_tests/settings.py
@@ -6,8 +6,6 @@ from django.utils._os import upath
 
 TEST_ROOT = os.path.dirname(upath(__file__))
 
-TESTFILES_PATH = os.path.join(TEST_ROOT, 'apps', 'test', 'static', 'test')
-
 TEST_SETTINGS = {
     'DEBUG': True,
     'MEDIA_URL': '/media/',
diff --git a/tests/staticfiles_tests/test_management.py b/tests/staticfiles_tests/test_management.py
index 784e5b74fd..09557185ed 100644
--- a/tests/staticfiles_tests/test_management.py
+++ b/tests/staticfiles_tests/test_management.py
@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 import codecs
 import os
 import shutil
+import tempfile
 import unittest
 
 from django.conf import settings
@@ -11,6 +12,7 @@ from django.contrib.staticfiles.management.commands import collectstatic
 from django.core.exceptions import ImproperlyConfigured
 from django.core.management import call_command
 from django.test import override_settings
+from django.test.utils import extend_sys_path
 from django.utils import six
 from django.utils._os import symlinks_supported
 from django.utils.encoding import force_text
@@ -197,31 +199,45 @@ class TestCollectionFilesOverride(CollectionTestCase):
     Test overriding duplicated files by ``collectstatic`` management command.
     Check for proper handling of apps order in installed apps even if file modification
     dates are in different order:
-        'staticfiles_tests.apps.test',
+        'staticfiles_test_app',
         'staticfiles_tests.apps.no_label',
     """
     def setUp(self):
-        self.orig_path = os.path.join(TEST_ROOT, 'apps', 'no_label', 'static', 'file2.txt')
+        self.temp_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.temp_dir)
+
         # get modification and access times for no_label/static/file2.txt
+        self.orig_path = os.path.join(TEST_ROOT, 'apps', 'no_label', 'static', 'file2.txt')
         self.orig_mtime = os.path.getmtime(self.orig_path)
         self.orig_atime = os.path.getatime(self.orig_path)
 
-        # prepare duplicate of file2.txt from no_label app
+        # prepare duplicate of file2.txt from a temporary app
         # this file will have modification time older than no_label/static/file2.txt
-        # anyway it should be taken to STATIC_ROOT because 'test' app is before
+        # anyway it should be taken to STATIC_ROOT because the temporary app is before
         # 'no_label' app in installed apps
-        self.testfile_path = os.path.join(TEST_ROOT, 'apps', 'test', 'static', 'file2.txt')
+        self.temp_app_path = os.path.join(self.temp_dir, 'staticfiles_test_app')
+        self.testfile_path = os.path.join(self.temp_app_path, 'static', 'file2.txt')
+
+        os.makedirs(self.temp_app_path)
+        with open(os.path.join(self.temp_app_path, '__init__.py'), 'w+'):
+            pass
+
+        os.makedirs(os.path.dirname(self.testfile_path))
         with open(self.testfile_path, 'w+') as f:
             f.write('duplicate of file2.txt')
+
         os.utime(self.testfile_path, (self.orig_atime - 1, self.orig_mtime - 1))
+
+        self.settings_with_test_app = self.modify_settings(
+            INSTALLED_APPS={'prepend': 'staticfiles_test_app'})
+        with extend_sys_path(self.temp_dir):
+            self.settings_with_test_app.enable()
+
         super(TestCollectionFilesOverride, self).setUp()
 
     def tearDown(self):
-        if os.path.exists(self.testfile_path):
-            os.unlink(self.testfile_path)
-        # set back original modification time
-        os.utime(self.orig_path, (self.orig_atime, self.orig_mtime))
         super(TestCollectionFilesOverride, self).tearDown()
+        self.settings_with_test_app.disable()
 
     def test_ordering_override(self):
         """
@@ -234,22 +250,11 @@ class TestCollectionFilesOverride(CollectionTestCase):
 
         self.assertFileContains('file2.txt', 'duplicate of file2.txt')
 
-        # and now change modification time of no_label/static/file2.txt
-        # test app is first in installed apps so file2.txt should remain unmodified
-        mtime = os.path.getmtime(self.testfile_path)
-        atime = os.path.getatime(self.testfile_path)
-        os.utime(self.orig_path, (mtime + 1, atime + 1))
-
-        # run collectstatic again
-        self.run_collectstatic()
-
-        self.assertFileContains('file2.txt', 'duplicate of file2.txt')
-
 
 # The collectstatic test suite already has conflicting files since both
 # project/test/file.txt and apps/test/static/test/file.txt are collected. To
 # properly test for the warning not happening unless we tell it to explicitly,
-# we only include static files from the default finders.
+# we remove the project directory and will add back a conflicting file later.
 @override_settings(STATICFILES_DIRS=[])
 class TestCollectionOverwriteWarning(CollectionTestCase):
     """
@@ -268,41 +273,37 @@ class TestCollectionOverwriteWarning(CollectionTestCase):
         """
         out = six.StringIO()
         call_command('collectstatic', interactive=False, verbosity=3, stdout=out, **kwargs)
-        out.seek(0)
-        return out.read()
+        return force_text(out.getvalue())
 
     def test_no_warning(self):
         """
         There isn't a warning if there isn't a duplicate destination.
         """
         output = self._collectstatic_output(clear=True)
-        self.assertNotIn(self.warning_string, force_text(output))
+        self.assertNotIn(self.warning_string, output)
 
     def test_warning(self):
         """
         There is a warning when there are duplicate destinations.
         """
-        # Create new file in the no_label app that also exists in the test app.
-        test_dir = os.path.join(TEST_ROOT, 'apps', 'no_label', 'static', 'test')
-        if not os.path.exists(test_dir):
-            os.mkdir(test_dir)
+        static_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, static_dir)
 
-        try:
-            duplicate_path = os.path.join(test_dir, 'file.txt')
-            with open(duplicate_path, 'w+') as f:
-                f.write('duplicate of file.txt')
+        duplicate = os.path.join(static_dir, 'test', 'file.txt')
+        os.mkdir(os.path.dirname(duplicate))
+        with open(duplicate, 'w+') as f:
+            f.write('duplicate of file.txt')
+
+        with self.settings(STATICFILES_DIRS=[static_dir]):
             output = self._collectstatic_output(clear=True)
-            self.assertIn(self.warning_string, force_text(output))
-        finally:
-            if os.path.exists(duplicate_path):
-                os.unlink(duplicate_path)
+        self.assertIn(self.warning_string, output)
 
-        if os.path.exists(test_dir):
-            os.rmdir(test_dir)
+        os.remove(duplicate)
 
         # Make sure the warning went away again.
-        output = self._collectstatic_output(clear=True)
-        self.assertNotIn(self.warning_string, force_text(output))
+        with self.settings(STATICFILES_DIRS=[static_dir]):
+            output = self._collectstatic_output(clear=True)
+        self.assertNotIn(self.warning_string, output)
 
 
 @override_settings(STATICFILES_STORAGE='staticfiles_tests.storage.DummyStorage')
diff --git a/tests/staticfiles_tests/test_storage.py b/tests/staticfiles_tests/test_storage.py
index c3318512f6..b96d9d0f12 100644
--- a/tests/staticfiles_tests/test_storage.py
+++ b/tests/staticfiles_tests/test_storage.py
@@ -1,7 +1,9 @@
 from __future__ import unicode_literals
 
 import os
+import shutil
 import sys
+import tempfile
 import unittest
 
 from django.conf import settings
@@ -18,7 +20,7 @@ from django.utils.encoding import force_text
 from .cases import (
     BaseCollectionTestCase, BaseStaticFilesTestCase, StaticFilesTestCase,
 )
-from .settings import TEST_ROOT, TEST_SETTINGS, TESTFILES_PATH
+from .settings import TEST_ROOT, TEST_SETTINGS
 
 
 def hashed_file_path(test, path):
@@ -252,15 +254,25 @@ class TestCollectionManifestStorage(TestHashedFiles, BaseCollectionTestCase,
     def setUp(self):
         super(TestCollectionManifestStorage, self).setUp()
 
-        self._clear_filename = os.path.join(TESTFILES_PATH, 'cleared.txt')
+        temp_dir = tempfile.mkdtemp()
+        os.makedirs(os.path.join(temp_dir, 'test'))
+        self._clear_filename = os.path.join(temp_dir, 'test', 'cleared.txt')
         with open(self._clear_filename, 'w') as f:
             f.write('to be deleted in one test')
 
+        self.patched_settings = self.settings(
+            STATICFILES_DIRS=settings.STATICFILES_DIRS + [temp_dir])
+        self.patched_settings.enable()
+        self.addCleanup(shutil.rmtree, six.text_type(temp_dir))
+
     def tearDown(self):
-        super(TestCollectionManifestStorage, self).tearDown()
+        self.patched_settings.disable()
+
         if os.path.exists(self._clear_filename):
             os.unlink(self._clear_filename)
 
+        super(TestCollectionManifestStorage, self).tearDown()
+
     def test_manifest_exists(self):
         filename = storage.staticfiles_storage.manifest_name
         path = storage.staticfiles_storage.path(filename)

From ba813864870d63de1d1679271c38a3c15e94e934 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Fri, 6 Feb 2015 11:38:22 +0100
Subject: [PATCH 08/17] Introduced a mixin for serializing tests.

---
 django/test/testcases.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/django/test/testcases.py b/django/test/testcases.py
index fd93ba5bad..302c284edb 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -20,6 +20,7 @@ from django.apps import apps
 from django.conf import settings
 from django.core import mail
 from django.core.exceptions import ImproperlyConfigured, ValidationError
+from django.core.files import locks
 from django.core.handlers.wsgi import WSGIHandler, get_path_info
 from django.core.management import call_command
 from django.core.management.color import no_style
@@ -1379,3 +1380,31 @@ class LiveServerTestCase(TransactionTestCase):
     def tearDownClass(cls):
         cls._tearDownClassInternal()
         super(LiveServerTestCase, cls).tearDownClass()
+
+
+class SerializeMixin(object):
+    """
+    Mixin to enforce serialization of TestCases that share a common resource.
+
+    Define a common 'lockfile' for each set of TestCases to serialize. This
+    file must exist on the filesystem.
+
+    Place it early in the MRO in order to isolate setUpClass / tearDownClass.
+    """
+
+    lockfile = None
+
+    @classmethod
+    def setUpClass(cls):
+        if cls.lockfile is None:
+            raise ValueError(
+                "{}.lockfile isn't set. Set it to a unique value "
+                "in the base class.".format(cls.__name__))
+        cls._lockfile = open(cls.lockfile)
+        locks.lock(cls._lockfile, locks.LOCK_EX)
+        super(SerializeMixin, cls).setUpClass()
+
+    @classmethod
+    def tearDownClass(cls):
+        super(SerializeMixin, cls).tearDownClass()
+        cls._lockfile.close()

From b799a50c8e4461121b52659970c21a58b4067651 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 5 Feb 2015 22:33:13 +0100
Subject: [PATCH 09/17] Serialized some tests that interact with the
 filesystem.

Considering the APIs exercised by these test cases, it's hard to make
them independent.
---
 tests/i18n/test_extraction.py         | 16 ++++++++++------
 tests/model_fields/test_imagefield.py |  5 ++++-
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/tests/i18n/test_extraction.py b/tests/i18n/test_extraction.py
index 4a612c546b..b9c4b4fc3e 100644
--- a/tests/i18n/test_extraction.py
+++ b/tests/i18n/test_extraction.py
@@ -17,6 +17,7 @@ from django.core.management.commands.makemessages import \
     Command as MakeMessagesCommand
 from django.core.management.utils import find_command
 from django.test import SimpleTestCase, mock, override_settings
+from django.test.testcases import SerializeMixin
 from django.test.utils import captured_stderr, captured_stdout
 from django.utils import six
 from django.utils._os import upath
@@ -30,7 +31,13 @@ this_directory = os.path.dirname(upath(__file__))
 
 
 @skipUnless(has_xgettext, 'xgettext is mandatory for extraction tests')
-class ExtractorTests(SimpleTestCase):
+class ExtractorTests(SerializeMixin, SimpleTestCase):
+
+    # makemessages scans the current working directory and writes in the
+    # locale subdirectory. There aren't any options to control this. As a
+    # consequence tests can't run in parallel. Since i18n tests run in less
+    # than 4 seconds, serializing them with SerializeMixin is acceptable.
+    lockfile = __file__
 
     test_dir = os.path.abspath(os.path.join(this_directory, 'commands'))
 
@@ -610,9 +617,6 @@ class KeepPotFileExtractorTests(ExtractorTests):
 
     POT_FILE = 'locale/django.pot'
 
-    def setUp(self):
-        super(KeepPotFileExtractorTests, self).setUp()
-
     def tearDown(self):
         super(KeepPotFileExtractorTests, self).tearDown()
         os.chdir(self.test_dir)
@@ -646,6 +650,7 @@ class MultipleLocaleExtractionTests(ExtractorTests):
     LOCALES = ['pt', 'de', 'ch']
 
     def tearDown(self):
+        super(MultipleLocaleExtractionTests, self).tearDown()
         os.chdir(self.test_dir)
         for locale in self.LOCALES:
             try:
@@ -677,7 +682,6 @@ class ExcludedLocaleExtractionTests(ExtractorTests):
 
     def setUp(self):
         super(ExcludedLocaleExtractionTests, self).setUp()
-
         os.chdir(self.test_dir)  # ExtractorTests.tearDown() takes care of restoring.
         shutil.copytree('canned_locale', 'locale')
         self._set_times_for_all_po_files()
@@ -719,7 +723,7 @@ class ExcludedLocaleExtractionTests(ExtractorTests):
 class CustomLayoutExtractionTests(ExtractorTests):
 
     def setUp(self):
-        self._cwd = os.getcwd()
+        super(CustomLayoutExtractionTests, self).setUp()
         self.test_dir = os.path.join(this_directory, 'project_dir')
 
     def test_no_locale_raises(self):
diff --git a/tests/model_fields/test_imagefield.py b/tests/model_fields/test_imagefield.py
index c2908b06e4..8320fafaa8 100644
--- a/tests/model_fields/test_imagefield.py
+++ b/tests/model_fields/test_imagefield.py
@@ -8,6 +8,7 @@ from django.core.exceptions import ImproperlyConfigured
 from django.core.files import File
 from django.core.files.images import ImageFile
 from django.test import TestCase
+from django.test.testcases import SerializeMixin
 from django.utils._os import upath
 
 try:
@@ -27,11 +28,13 @@ else:
     PersonTwoImages = Person
 
 
-class ImageFieldTestMixin(object):
+class ImageFieldTestMixin(SerializeMixin):
     """
     Mixin class to provide common functionality to ImageField test classes.
     """
 
+    lockfile = __file__
+
     # Person model to use for tests.
     PersonModel = PersonWithHeightAndWidth
     # File class to use for file instances.

From 073ea9e8522e7d685864fd9e283bd1fcb9fa5243 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Fri, 5 Jun 2015 16:44:12 +0200
Subject: [PATCH 10/17] Acknoweldeged a limitation of the parallel test runner.

Notably it will fail to report a Model.DoesNotExist exceptions because
the class itself isn't pickleable. (Django has specific code to make its
instances pickleable.)
---
 django/test/runner.py     | 54 +++++++++++++++++++++++++++++++++++++++
 docs/ref/django-admin.txt | 11 ++++++++
 2 files changed, 65 insertions(+)

diff --git a/django/test/runner.py b/django/test/runner.py
index cd12d6203f..0d01b9b61d 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -4,6 +4,8 @@ import itertools
 import logging
 import multiprocessing
 import os
+import pickle
+import textwrap
 import unittest
 from importlib import import_module
 
@@ -82,6 +84,55 @@ class RemoteTestResult(object):
     def test_index(self):
         return self.testsRun - 1
 
+    def check_pickleable(self, test, err):
+        # Ensure that sys.exc_info() tuples are picklable. This displays a
+        # clear multiprocessing.pool.RemoteTraceback generated in the child
+        # process instead of a multiprocessing.pool.MaybeEncodingError, making
+        # the root cause easier to figure out for users who aren't familiar
+        # with the multiprocessing module. Since we're in a forked process,
+        # our best chance to communicate with them is to print to stdout.
+        try:
+            pickle.dumps(err)
+        except Exception as exc:
+            original_exc_txt = repr(err[1])
+            original_exc_txt = textwrap.fill(original_exc_txt, 75)
+            original_exc_txt = textwrap.indent(original_exc_txt, '    ')
+            pickle_exc_txt = repr(exc)
+            pickle_exc_txt = textwrap.fill(pickle_exc_txt, 75)
+            pickle_exc_txt = textwrap.indent(pickle_exc_txt, '    ')
+            if tblib is None:
+                print("""
+
+{} failed:
+
+{}
+
+Unfortunately, tracebacks cannot be pickled, making it impossible for the
+parallel test runner to handle this exception cleanly.
+
+In order to see the traceback, you should install tblib:
+
+    pip install tblib
+""".format(test, original_exc_txt))
+            else:
+                print("""
+
+{} failed:
+
+{}
+
+Unfortunately, the exception it raised cannot be pickled, making it impossible
+for the parallel test runner to handle it cleanly.
+
+Here's the error encountered while trying to pickle the exception:
+
+{}
+
+You should re-run this test without the --parallel option to reproduce the
+failure and get a correct traceback.
+""".format(test, original_exc_txt, pickle_exc_txt))
+            raise
+
     def stop_if_failfast(self):
         if self.failfast:
             self.stop()
@@ -103,10 +154,12 @@ class RemoteTestResult(object):
         self.events.append(('stopTest', self.test_index))
 
     def addError(self, test, err):
+        self.check_pickleable(test, err)
         self.events.append(('addError', self.test_index, err))
         self.stop_if_failfast()
 
     def addFailure(self, test, err):
+        self.check_pickleable(test, err)
         self.events.append(('addFailure', self.test_index, err))
         self.stop_if_failfast()
 
@@ -120,6 +173,7 @@ class RemoteTestResult(object):
         self.events.append(('addSkip', self.test_index, reason))
 
     def addExpectedFailure(self, test, err):
+        self.check_pickleable(test, err)
         self.events.append(('addExpectedFailure', self.test_index, err))
 
     def addUnexpectedSuccess(self, test):
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index a98b60b45f..0c88b5aadb 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1285,6 +1285,17 @@ correctly:
 
     $ pip install tblib
 
+.. warning::
+
+    When test parallelization is enabled and a test fails, Django may be
+    unable to display the exception traceback. This can make debugging
+    difficult. If you encounter this problem, run the affected test without
+    parallelization to see the traceback of the failure.
+
+    This is a known limitation. It arises from the need to serialize objects
+    in order to exchange them between processes. See
+    :ref:`python:pickle-picklable` for details.
+
 testserver <fixture fixture ...>
 --------------------------------
 

From 0bd58e0efb388726731dd0c85c5e050b5b280a0f Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Sun, 30 Aug 2015 10:50:10 +0200
Subject: [PATCH 11/17] Test parallelization isn't implemented on Oracle.

---
 docs/ref/django-admin.txt | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 0c88b5aadb..4a7b03de43 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1285,6 +1285,8 @@ correctly:
 
     $ pip install tblib
 
+This feature isn't available on Oracle.
+
 .. warning::
 
     When test parallelization is enabled and a test fails, Django may be

From e8b49d4cc4056716195f16963c9bb57e87952e0b Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Mon, 7 Sep 2015 22:59:13 +0200
Subject: [PATCH 12/17] Propagated database clone settings to new connections.

---
 django/test/runner.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/django/test/runner.py b/django/test/runner.py
index 0d01b9b61d..2619fe4504 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -233,7 +233,11 @@ def _init_worker(counter):
     for alias in connections:
         connection = connections[alias]
         settings_dict = connection.creation.get_test_db_clone_settings(_worker_id)
-        connection.settings_dict = settings_dict
+        # connection.settings_dict must be updated in place for changes to be
+        # reflected in django.db.connections. If the following line assigned
+        # connection.settings_dict = settings_dict, new threads would connect
+        # to the default database instead of the appropriate clone.
+        connection.settings_dict.update(settings_dict)
         connection.close()
 
 

From 05cea7fdbbcd7bdcdc8d8162d95b1dd5d8195913 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Mon, 7 Sep 2015 22:10:31 +0200
Subject: [PATCH 13/17] Changed database connection duplication technique.

This new technique is more straightforward and compatible with test
parallelization, where the effective database connection settings no
longer match settings.DATABASES.
---
 django/db/backends/base/base.py  | 14 ++++++++++++++
 tests/backends/tests.py          | 26 +++++++++-----------------
 tests/delete_regress/tests.py    |  7 ++-----
 tests/select_for_update/tests.py |  7 ++-----
 4 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/django/db/backends/base/base.py b/django/db/backends/base/base.py
index 96ca0ccfde..2e6a528171 100644
--- a/django/db/backends/base/base.py
+++ b/django/db/backends/base/base.py
@@ -1,3 +1,4 @@
+import copy
 import time
 import warnings
 from collections import deque
@@ -622,3 +623,16 @@ class BaseDatabaseWrapper(object):
                 func()
         finally:
             self.run_on_commit = []
+
+    def copy(self, alias=None, allow_thread_sharing=None):
+        """
+        Return a copy of this connection.
+
+        For tests that require two connections to the same database.
+        """
+        settings_dict = copy.deepcopy(self.settings_dict)
+        if alias is None:
+            alias = self.alias
+        if allow_thread_sharing is None:
+            allow_thread_sharing = self.allow_thread_sharing
+        return type(self)(settings_dict, alias, allow_thread_sharing)
diff --git a/tests/backends/tests.py b/tests/backends/tests.py
index ed42d6317a..c0af1bdb60 100644
--- a/tests/backends/tests.py
+++ b/tests/backends/tests.py
@@ -2,7 +2,6 @@
 # Unit and doctests for specific database backends.
 from __future__ import unicode_literals
 
-import copy
 import datetime
 import re
 import threading
@@ -10,7 +9,6 @@ import unittest
 import warnings
 from decimal import Decimal, Rounded
 
-from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.management.color import no_style
 from django.db import (
@@ -182,8 +180,8 @@ class PostgreSQLTests(TestCase):
                 nodb_conn = connection._nodb_connection
         del connection._nodb_connection
         self.assertIsNotNone(nodb_conn.settings_dict['NAME'])
-        self.assertEqual(nodb_conn.settings_dict['NAME'], settings.DATABASES[DEFAULT_DB_ALIAS]['NAME'])
-        # Check a RuntimeWarning nas been emitted
+        self.assertEqual(nodb_conn.settings_dict['NAME'], connection.settings_dict['NAME'])
+        # Check a RuntimeWarning has been emitted
         self.assertEqual(len(w), 1)
         self.assertEqual(w[0].message.__class__, RuntimeWarning)
 
@@ -219,9 +217,7 @@ class PostgreSQLTests(TestCase):
         PostgreSQL shouldn't roll back SET TIME ZONE, even if the first
         transaction is rolled back (#17062).
         """
-        databases = copy.deepcopy(settings.DATABASES)
-        new_connections = ConnectionHandler(databases)
-        new_connection = new_connections[DEFAULT_DB_ALIAS]
+        new_connection = connection.copy()
 
         try:
             # Ensure the database default time zone is different than
@@ -258,10 +254,9 @@ class PostgreSQLTests(TestCase):
         The connection wrapper shouldn't believe that autocommit is enabled
         after setting the time zone when AUTOCOMMIT is False (#21452).
         """
-        databases = copy.deepcopy(settings.DATABASES)
-        databases[DEFAULT_DB_ALIAS]['AUTOCOMMIT'] = False
-        new_connections = ConnectionHandler(databases)
-        new_connection = new_connections[DEFAULT_DB_ALIAS]
+        new_connection = connection.copy()
+        new_connection.settings_dict['AUTOCOMMIT'] = False
+
         try:
             # Open a database connection.
             new_connection.cursor()
@@ -285,10 +280,8 @@ class PostgreSQLTests(TestCase):
         # Check the level on the psycopg2 connection, not the Django wrapper.
         self.assertEqual(connection.connection.isolation_level, read_committed)
 
-        databases = copy.deepcopy(settings.DATABASES)
-        databases[DEFAULT_DB_ALIAS]['OPTIONS']['isolation_level'] = serializable
-        new_connections = ConnectionHandler(databases)
-        new_connection = new_connections[DEFAULT_DB_ALIAS]
+        new_connection = connection.copy()
+        new_connection.settings_dict['OPTIONS']['isolation_level'] = serializable
         try:
             # Start a transaction so the isolation level isn't reported as 0.
             new_connection.set_autocommit(False)
@@ -748,8 +741,7 @@ class BackendTestCase(TransactionTestCase):
         """
         old_queries_limit = BaseDatabaseWrapper.queries_limit
         BaseDatabaseWrapper.queries_limit = 3
-        new_connections = ConnectionHandler(settings.DATABASES)
-        new_connection = new_connections[DEFAULT_DB_ALIAS]
+        new_connection = connection.copy()
 
         # Initialize the connection and clear initialization statements.
         with new_connection.cursor():
diff --git a/tests/delete_regress/tests.py b/tests/delete_regress/tests.py
index 7cbd94f427..2128733798 100644
--- a/tests/delete_regress/tests.py
+++ b/tests/delete_regress/tests.py
@@ -2,9 +2,7 @@ from __future__ import unicode_literals
 
 import datetime
 
-from django.conf import settings
-from django.db import DEFAULT_DB_ALIAS, models, transaction
-from django.db.utils import ConnectionHandler
+from django.db import connection, models, transaction
 from django.test import TestCase, TransactionTestCase, skipUnlessDBFeature
 
 from .models import (
@@ -24,8 +22,7 @@ class DeleteLockingTest(TransactionTestCase):
 
     def setUp(self):
         # Create a second connection to the default database
-        new_connections = ConnectionHandler(settings.DATABASES)
-        self.conn2 = new_connections[DEFAULT_DB_ALIAS]
+        self.conn2 = connection.copy()
         self.conn2.set_autocommit(False)
 
     def tearDown(self):
diff --git a/tests/select_for_update/tests.py b/tests/select_for_update/tests.py
index af408f8ffe..70cd21d594 100644
--- a/tests/select_for_update/tests.py
+++ b/tests/select_for_update/tests.py
@@ -5,9 +5,7 @@ import time
 
 from multiple_database.routers import TestRouter
 
-from django.conf import settings
-from django.db import connection, router, transaction
-from django.db.utils import DEFAULT_DB_ALIAS, ConnectionHandler, DatabaseError
+from django.db import DatabaseError, connection, router, transaction
 from django.test import (
     TransactionTestCase, override_settings, skipIfDBFeature,
     skipUnlessDBFeature,
@@ -30,8 +28,7 @@ class SelectForUpdateTests(TransactionTestCase):
 
         # We need another database connection in transaction to test that one
         # connection issuing a SELECT ... FOR UPDATE will block.
-        new_connections = ConnectionHandler(settings.DATABASES)
-        self.new_connection = new_connections[DEFAULT_DB_ALIAS]
+        self.new_connection = connection.copy()
 
     def tearDown(self):
         try:

From 39bb66baad1b98e0fa10d668a09154a0f5372b3d Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Fri, 4 Sep 2015 23:22:56 +0200
Subject: [PATCH 14/17] Made it easier to customize the parallel test runner.

Subclass private APIs is marginally better than monkey-patching them,
even if it doesn't make a big difference in practice.
---
 django/test/runner.py | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/django/test/runner.py b/django/test/runner.py
index 2619fe4504..04ee14ec72 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -270,6 +270,10 @@ class ParallelTestSuite(unittest.TestSuite):
     that they have been run in parallel.
     """
 
+    # In case someone wants to modify these in a subclass.
+    init_worker = _init_worker
+    run_subsuite = _run_subsuite
+
     def __init__(self, suite, processes, failfast=False):
         self.subsuites = partition_suite_by_case(suite)
         self.processes = processes
@@ -297,13 +301,13 @@ class ParallelTestSuite(unittest.TestSuite):
         counter = multiprocessing.Value(ctypes.c_int, 0)
         pool = multiprocessing.Pool(
             processes=self.processes,
-            initializer=_init_worker,
+            initializer=self.init_worker.__func__,
             initargs=[counter])
         args = [
             (index, subsuite, self.failfast)
             for index, subsuite in enumerate(self.subsuites)
         ]
-        test_results = pool.imap_unordered(_run_subsuite, args)
+        test_results = pool.imap_unordered(self.run_subsuite.__func__, args)
 
         while True:
             if result.shouldStop:
@@ -339,6 +343,7 @@ class DiscoverRunner(object):
     """
 
     test_suite = unittest.TestSuite
+    parallel_test_suite = ParallelTestSuite
     test_runner = unittest.TextTestRunner
     test_loader = unittest.defaultTestLoader
     reorder_by = (TestCase, SimpleTestCase)
@@ -448,7 +453,7 @@ class DiscoverRunner(object):
         suite = reorder_suite(suite, self.reorder_by, self.reverse)
 
         if self.parallel > 1:
-            suite = ParallelTestSuite(suite, self.parallel, self.failfast)
+            suite = self.parallel_test_suite(suite, self.parallel, self.failfast)
 
         return suite
 

From 33c7c2a55770fe8ccc297a8ae13e04487b72b3a1 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Sun, 6 Sep 2015 11:12:08 +0200
Subject: [PATCH 15/17] Enabled parallel testing by default in runtests.py.

---
 django/db/backends/base/features.py           |  4 ++++
 django/db/backends/mysql/features.py          |  1 +
 django/db/backends/postgresql/features.py     |  1 +
 django/db/backends/sqlite3/features.py        |  1 +
 .../contributing/writing-code/unit-tests.txt  | 13 +++++++++++
 docs/releases/1.9.txt                         |  7 +++++-
 tests/requirements/base.txt                   |  1 +
 tests/runtests.py                             | 23 +++++++++++++++----
 8 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index b7861865ac..095164770f 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -212,6 +212,10 @@ class BaseDatabaseFeatures(object):
     # every expression is null?
     greatest_least_ignores_nulls = False
 
+    # Can the backend clone databases for parallel test execution?
+    # Defaults to False to allow third-party backends to opt-in.
+    can_clone_databases = False
+
     def __init__(self, connection):
         self.connection = connection
 
diff --git a/django/db/backends/mysql/features.py b/django/db/backends/mysql/features.py
index 8f2e99a791..c8ea8f7fb6 100644
--- a/django/db/backends/mysql/features.py
+++ b/django/db/backends/mysql/features.py
@@ -31,6 +31,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_release_savepoints = True
     atomic_transactions = False
     supports_column_check_constraints = False
+    can_clone_databases = True
 
     @cached_property
     def _mysql_storage_engine(self):
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index a07700e601..9130a4521e 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -28,3 +28,4 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_case_insensitive_like = False
     requires_sqlparse_for_splitting = False
     greatest_least_ignores_nulls = True
+    can_clone_databases = True
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 5697b8b7eb..dffc48afb8 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -37,6 +37,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_rollback_ddl = True
     supports_paramstyle_pyformat = False
     supports_sequence_reset = False
+    can_clone_databases = True
 
     @cached_property
     def uses_savepoints(self):
diff --git a/docs/internals/contributing/writing-code/unit-tests.txt b/docs/internals/contributing/writing-code/unit-tests.txt
index 8a097bba8c..55e3a2d5c7 100644
--- a/docs/internals/contributing/writing-code/unit-tests.txt
+++ b/docs/internals/contributing/writing-code/unit-tests.txt
@@ -284,3 +284,16 @@ combine this with ``--verbosity=2``, all SQL queries will be output::
 .. versionadded:: 1.8
 
     The ``--reverse`` and ``--debug-sql`` options were added.
+
+By default tests are run in parallel with one process per core. You can adjust
+this behavior with the ``--parallel`` option::
+
+    $ ./runtests.py basic --parallel=1
+
+You can also use the ``DJANGO_TEST_PROCESSES`` environment variable for this
+purpose.
+
+.. versionadded:: 1.9
+
+    Support for running tests in parallel and the ``--parallel`` option were
+    added.
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index 99b6e44bc3..41e7701e99 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -135,6 +135,10 @@ Each process gets its own database. You must ensure that different test cases
 don't access the same resources. For instance, test cases that touch the
 filesystem should create a temporary directory for their own use.
 
+This option is enabled by default for Django's own test suite on database
+backends that support it (this is all the built-in backends except for
+Oracle).
+
 Minor features
 ~~~~~~~~~~~~~~
 
@@ -686,7 +690,8 @@ Database backend API
   and hasn't been called anywhere in Django's code or tests.
 
 * In order to support test parallelization, you must implement the
-  ``DatabaseCreation._clone_test_db()`` method. You may have to adjust
+  ``DatabaseCreation._clone_test_db()`` method and set
+  ``DatabaseFeatures.can_clone_databases = True``. You may have to adjust
   ``DatabaseCreation.get_test_db_clone_settings()``.
 
 Default settings that were tuples are now lists
diff --git a/tests/requirements/base.txt b/tests/requirements/base.txt
index af828306c3..845aefbb87 100644
--- a/tests/requirements/base.txt
+++ b/tests/requirements/base.txt
@@ -8,3 +8,4 @@ PyYAML
 pytz > dev
 selenium
 sqlparse
+tblib
diff --git a/tests/runtests.py b/tests/runtests.py
index 0577737a5f..cfc8722ae2 100755
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -12,7 +12,7 @@ from argparse import ArgumentParser
 import django
 from django.apps import apps
 from django.conf import settings
-from django.db import connection
+from django.db import connection, connections
 from django.test import TestCase, TransactionTestCase
 from django.test.runner import default_test_processes
 from django.test.utils import get_runner
@@ -103,8 +103,10 @@ def get_installed():
 
 def setup(verbosity, test_labels, parallel):
     if verbosity >= 1:
-        print("Testing against Django installed in '%s' with %d processes" % (
-            os.path.dirname(django.__file__), parallel))
+        msg = "Testing against Django installed in '%s'" % os.path.dirname(django.__file__)
+        if parallel > 1:
+            msg += " with %d processes" % parallel
+        print(msg)
 
     # Force declaring available_apps in TransactionTestCase for faster tests.
     def no_available_apps(self):
@@ -232,6 +234,17 @@ def teardown(state):
         setattr(settings, key, value)
 
 
+def actual_test_processes(parallel):
+    if parallel == 0:
+        # This doesn't work before django.setup() on some databases.
+        if all(conn.features.can_clone_databases for conn in connections.all()):
+            return default_test_processes()
+        else:
+            return 1
+    else:
+        return parallel
+
+
 def django_tests(verbosity, interactive, failfast, keepdb, reverse,
                  test_labels, debug_sql, parallel):
     state = setup(verbosity, test_labels, parallel)
@@ -249,7 +262,7 @@ def django_tests(verbosity, interactive, failfast, keepdb, reverse,
         keepdb=keepdb,
         reverse=reverse,
         debug_sql=debug_sql,
-        parallel=parallel,
+        parallel=actual_test_processes(parallel),
     )
     failures = test_runner.run_tests(
         test_labels or get_installed(),
@@ -396,7 +409,7 @@ if __name__ == "__main__":
         '--debug-sql', action='store_true', dest='debug_sql', default=False,
         help='Turn on the SQL query logger within tests.')
     parser.add_argument(
-        '--parallel', dest='parallel', nargs='?', default=1, type=int,
+        '--parallel', dest='parallel', nargs='?', default=0, type=int,
         const=default_test_processes(),
         help='Run tests in parallel processes.')
 

From 710b4a70321148b470bf55c73d81170f07c839f9 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 10 Sep 2015 14:06:06 +0200
Subject: [PATCH 16/17] Avoided running more test processes than necessary.

This reduces the time spent cloning databases.

Thanks Tim for the suggestion.
---
 django/test/runner.py     | 12 +++++++++++-
 docs/ref/django-admin.txt |  4 ++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/django/test/runner.py b/django/test/runner.py
index 04ee14ec72..243ab714a4 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -453,7 +453,17 @@ class DiscoverRunner(object):
         suite = reorder_suite(suite, self.reorder_by, self.reverse)
 
         if self.parallel > 1:
-            suite = self.parallel_test_suite(suite, self.parallel, self.failfast)
+            parallel_suite = self.parallel_test_suite(suite, self.parallel, self.failfast)
+
+            # Since tests are distributed across processes on a per-TestCase
+            # basis, there's no need for more processes than TestCases.
+            parallel_units = len(parallel_suite.subsuites)
+            if self.parallel > parallel_units:
+                self.parallel = parallel_units
+
+            # If there's only one TestCase, parallelization isn't needed.
+            if self.parallel > 1:
+                suite = parallel_suite
 
         return suite
 
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 4a7b03de43..dff48ac460 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1274,6 +1274,10 @@ By default ``--parallel`` runs one process per core according to
 either by providing it as the option's value, e.g. ``--parallel=4``, or by
 setting the ``DJANGO_TEST_PROCESSES`` environment variable.
 
+Django distributes test cases — :class:`unittest.TestCase` subclasses — to
+subprocesses. If there are fewer test cases than configured processes, Django
+will reduce the number of processes accordingly.
+
 Each process gets its own database. You must ensure that different test cases
 don't access the same resources. For instance, test cases that touch the
 filesystem should create a temporary directory for their own use.

From a32206b3650c5ce18c0a06eb0eb40abc8becfa58 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Thu, 10 Sep 2015 15:41:26 +0200
Subject: [PATCH 17/17] Documented that the parallel test runner doesn't work
 on Windows.

---
 docs/ref/django-admin.txt | 3 ++-
 docs/releases/1.9.txt     | 7 ++++---
 tests/runtests.py         | 5 ++++-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index dff48ac460..26702d7db7 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -1289,7 +1289,8 @@ correctly:
 
     $ pip install tblib
 
-This feature isn't available on Oracle.
+This feature isn't available on Windows. It doesn't work with the Oracle
+database backend either.
 
 .. warning::
 
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index 41e7701e99..3d256ae29d 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -135,9 +135,10 @@ Each process gets its own database. You must ensure that different test cases
 don't access the same resources. For instance, test cases that touch the
 filesystem should create a temporary directory for their own use.
 
-This option is enabled by default for Django's own test suite on database
-backends that support it (this is all the built-in backends except for
-Oracle).
+This option is enabled by default for Django's own test suite provided:
+
+- the OS supports it (all but Windows)
+- the database backend supports it (all the built-in backends but Oracle)
 
 Minor features
 ~~~~~~~~~~~~~~
diff --git a/tests/runtests.py b/tests/runtests.py
index cfc8722ae2..4d6e22e3b2 100755
--- a/tests/runtests.py
+++ b/tests/runtests.py
@@ -236,8 +236,11 @@ def teardown(state):
 
 def actual_test_processes(parallel):
     if parallel == 0:
+        # On Python 3.4+: if multiprocessing.get_start_method() != 'fork':
+        if not hasattr(os, 'fork'):
+            return 1
         # This doesn't work before django.setup() on some databases.
-        if all(conn.features.can_clone_databases for conn in connections.all()):
+        elif all(conn.features.can_clone_databases for conn in connections.all()):
             return default_test_processes()
         else:
             return 1