diff --git a/django/core/cache/backends/dummy.py b/django/core/cache/backends/dummy.py
index 7957df8072..ab2b838ad4 100644
--- a/django/core/cache/backends/dummy.py
+++ b/django/core/cache/backends/dummy.py
@@ -25,19 +25,10 @@ class DummyCache(BaseCache):
         key = self.make_key(key, version=version)
         self.validate_key(key)
 
-    def get_many(self, keys, version=None):
-        return {}
-
     def has_key(self, key, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
         return False
 
-    def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None):
-        return []
-
-    def delete_many(self, keys, version=None):
-        pass
-
     def clear(self):
         pass
diff --git a/tests/cache/tests.py b/tests/cache/tests.py
index 5cee2d84a5..63e0c8a02e 100644
--- a/tests/cache/tests.py
+++ b/tests/cache/tests.py
@@ -59,6 +59,12 @@ class Unpicklable:
         raise pickle.PickleError()
 
 
+KEY_ERRORS_WITH_MEMCACHED_MSG = (
+    'Cache key contains characters that will cause errors if used with '
+    'memcached: %r'
+)
+
+
 @override_settings(CACHES={
     'default': {
         'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
@@ -94,6 +100,10 @@ class DummyCacheTests(SimpleTestCase):
         self.assertEqual(cache.get_many(['a', 'c', 'd']), {})
         self.assertEqual(cache.get_many(['a', 'b', 'e']), {})
 
+    def test_get_many_invalid_key(self):
+        with self.assertWarns(CacheKeyWarning, msg=KEY_ERRORS_WITH_MEMCACHED_MSG % 'key with spaces'):
+            cache.get_many(['key with spaces'])
+
     def test_delete(self):
         "Cache deletion is transparently ignored on the dummy cache backend"
         cache.set("key1", "spam")
@@ -176,10 +186,18 @@ class DummyCacheTests(SimpleTestCase):
         self.assertEqual(cache.set_many({'a': 1, 'b': 2}), [])
         self.assertEqual(cache.set_many({'a': 1, 'b': 2}, timeout=2, version='1'), [])
 
+    def test_set_many_invalid_key(self):
+        with self.assertWarns(CacheKeyWarning, msg=KEY_ERRORS_WITH_MEMCACHED_MSG % 'key with spaces'):
+            cache.set_many({'key with spaces': 'foo'})
+
     def test_delete_many(self):
         "delete_many does nothing for the dummy cache backend"
         cache.delete_many(['a', 'b'])
 
+    def test_delete_many_invalid_key(self):
+        with self.assertWarns(CacheKeyWarning, msg=KEY_ERRORS_WITH_MEMCACHED_MSG % 'key with spaces'):
+            cache.delete_many({'key with spaces': 'foo'})
+
     def test_clear(self):
         "clear does nothing for the dummy cache backend"
         cache.clear()
@@ -596,11 +614,7 @@ class BaseCacheTests:
     def test_invalid_key_characters(self):
         # memcached doesn't allow whitespace or control characters in keys.
         key = 'key with spaces and 清'
-        expected_warning = (
-            "Cache key contains characters that will cause errors if used "
-            "with memcached: %r" % key
-        )
-        self._perform_invalid_key_test(key, expected_warning)
+        self._perform_invalid_key_test(key, KEY_ERRORS_WITH_MEMCACHED_MSG % key)
 
     def test_invalid_key_length(self):
         # memcached limits key length to 250.