Disable frozen dicts by default

changelog.d/3987.misc

@@ -0,0 +1 @@
+Disable USE_FROZEN_DICTS for unittests by default.

tests/utils.py

@@ -48,6 +48,9 @@
 POSTGRES_USER = os.environ.get("SYNAPSE_POSTGRES_USER", "postgres")
 POSTGRES_BASE_DB = "_synapse_unit_tests_base_%s" % (os.getpid(),)
 
+# Disable frozendicts by default, but enable if the environment var is set.
+USE_FROZEN_DICTS = os.environ.get("SYNAPSE_USE_FROZEN_DICTS", False)
+
 
 def setupdb():
 
@@ -136,6 +139,9 @@ def default_config(name):
     config.rc_messages_per_second = 10000
     config.rc_message_burst_count = 10000
 
+    # Use frozendicts if they're asked for.
+    config.use_frozen_dicts = bool(USE_FROZEN_DICTS)
+
     # we need a sane default_room_version, otherwise attempts to create rooms will
     # fail.
     config.default_room_version = "1"
@@ -182,7 +188,6 @@ def setup_test_homeserver(
     if config is None:
         config = default_config(name)
 
-    config.use_frozen_dicts = True
     config.ldap_enabled = False
 
     if "clock" not in kargs: