[2.0.x] Refs #27318 -- Made DummyCache.set_many() return a list for consistency…

[2.0.x] Refs #27318 -- Made DummyCache.set_many() return a list for consistency with other backends.

Backport of abacd09f from master

django/core/cache/backends/dummy.py

@@ -34,7 +34,7 @@ class DummyCache(BaseCache):
         return False
 
     def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None):
-        pass
+        return []
 
     def delete_many(self, keys, version=None):
         pass

tests/cache/tests.py

@@ -175,8 +175,8 @@ class DummyCacheTests(SimpleTestCase):
 
     def test_set_many(self):
         "set_many does nothing for the dummy cache backend"
-        cache.set_many({'a': 1, 'b': 2})
-        cache.set_many({'a': 1, 'b': 2}, timeout=2, version='1')
+        self.assertEqual(cache.set_many({'a': 1, 'b': 2}), [])
+        self.assertEqual(cache.set_many({'a': 1, 'b': 2}, timeout=2, version='1'), [])
 
     def test_delete_many(self):
         "delete_many does nothing for the dummy cache backend"