Reset global cache state before cache tests. (#11036)

This reverts #11019 and structures the code a bit more like it was before #10985.

The global cache state must be reset before running the tests since other test
cases might have configured caching (and thus touched the global state).

changelog.d/11036.misc

+Ensure that cache config tests do not share state.

tests/config/test_cache.py

@@ -12,25 +12,23 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from unittest.mock import patch
-
 from synapse.config.cache import CacheConfig, add_resizable_cache
 from synapse.util.caches.lrucache import LruCache
 
 from tests.unittest import TestCase
 
 
-# Patch the global _CACHES so that each test runs against its own state.
-@patch("synapse.config.cache._CACHES", new_callable=dict)
 class CacheConfigTests(TestCase):
     def setUp(self):
-        # Reset caches before each test
+        # Reset caches before each test since there's global state involved.
         self.config = CacheConfig()
+        self.config.reset()
 
     def tearDown(self):
+        # Also reset the caches after each test to leave state pristine.
         self.config.reset()
 
-    def test_individual_caches_from_environ(self, _caches):
+    def test_individual_caches_from_environ(self):
         """
         Individual cache factors will be loaded from the environment.
         """
@@ -43,7 +41,7 @@ class CacheConfigTests(TestCase):
 
         self.assertEqual(dict(self.config.cache_factors), {"something_or_other": 2.0})
 
-    def test_config_overrides_environ(self, _caches):
+    def test_config_overrides_environ(self):
         """
         Individual cache factors defined in the environment will take precedence
         over those in the config.
@@ -60,7 +58,7 @@ class CacheConfigTests(TestCase):
             {"foo": 1.0, "bar": 3.0, "something_or_other": 2.0},
         )
 
-    def test_individual_instantiated_before_config_load(self, _caches):
+    def test_individual_instantiated_before_config_load(self):
         """
         If a cache is instantiated before the config is read, it will be given
         the default cache size in the interim, and then resized once the config
@@ -76,7 +74,7 @@ class CacheConfigTests(TestCase):
 
         self.assertEqual(cache.max_size, 300)
 
-    def test_individual_instantiated_after_config_load(self, _caches):
+    def test_individual_instantiated_after_config_load(self):
         """
         If a cache is instantiated after the config is read, it will be
         immediately resized to the correct size given the per_cache_factor if
@@ -89,7 +87,7 @@ class CacheConfigTests(TestCase):
         add_resizable_cache("foo", cache_resize_callback=cache.set_cache_factor)
         self.assertEqual(cache.max_size, 200)
 
-    def test_global_instantiated_before_config_load(self, _caches):
+    def test_global_instantiated_before_config_load(self):
         """
         If a cache is instantiated before the config is read, it will be given
         the default cache size in the interim, and then resized to the new
@@ -104,7 +102,7 @@ class CacheConfigTests(TestCase):
 
         self.assertEqual(cache.max_size, 400)
 
-    def test_global_instantiated_after_config_load(self, _caches):
+    def test_global_instantiated_after_config_load(self):
         """
         If a cache is instantiated after the config is read, it will be
         immediately resized to the correct size given the global factor if there
@@ -117,7 +115,7 @@ class CacheConfigTests(TestCase):
         add_resizable_cache("foo", cache_resize_callback=cache.set_cache_factor)
         self.assertEqual(cache.max_size, 150)
 
-    def test_cache_with_asterisk_in_name(self, _caches):
+    def test_cache_with_asterisk_in_name(self):
         """Some caches have asterisks in their name, test that they are set correctly."""
 
         config = {
@@ -143,7 +141,7 @@ class CacheConfigTests(TestCase):
         add_resizable_cache("*cache_c*", cache_resize_callback=cache_c.set_cache_factor)
         self.assertEqual(cache_c.max_size, 200)
 
-    def test_apply_cache_factor_from_config(self, _caches):
+    def test_apply_cache_factor_from_config(self):
         """Caches can disable applying cache factor updates, mainly used by
         event cache size.
         """