Use a regular HomeServerConfig object for unit tests

Rather than using a Mock for the homeserver config, use a genuine
HomeServerConfig object. This makes for a more realistic test, and means that
we don't have to keep remembering to add things to the mock config every time
we add a new config setting.

tests/utils.py

@@ -28,7 +28,7 @@ from twisted.internet import defer, reactor
 
 from synapse.api.constants import EventTypes, RoomVersions
 from synapse.api.errors import CodeMessageException, cs_error
-from synapse.config.server import ServerConfig
+from synapse.config.homeserver import HomeServerConfig
 from synapse.federation.transport import server as federation_server
 from synapse.http.server import HttpServer
 from synapse.server import HomeServer
@@ -111,14 +111,25 @@ def default_config(name):
     """
     Create a reasonable test config.
     """
-    config = Mock()
-    config.signing_key = [MockKey()]
+    config_dict = {
+        "server_name": name,
+        "media_store_path": "media",
+        "uploads_path": "uploads",
+
+        # the test signing key is just an arbitrary ed25519 key to keep the config
+        # parser happy
+        "signing_key": "ed25519 a_lPym qvioDNmfExFBRPgdTU+wtFYKq4JfwFRv7sYVgWvmgJg",
+    }
+
+    config = HomeServerConfig()
+    config.parse_config_dict(config_dict)
+
+    # TODO: move this stuff into config_dict or get rid of it
     config.event_cache_size = 1
     config.enable_registration = True
     config.enable_registration_captcha = False
     config.macaroon_secret_key = "not even a little secret"
     config.expire_access_token = False
-    config.server_name = name
     config.trusted_third_party_id_servers = []
     config.room_invite_state_types = []
     config.password_providers = []
@@ -176,13 +187,6 @@ def default_config(name):
     # background, which upsets the test runner.
     config.update_user_directory = False
 
-    def is_threepid_reserved(threepid):
-        return ServerConfig.is_threepid_reserved(
-            config.mau_limits_reserved_threepids, threepid
-        )
-
-    config.is_threepid_reserved.side_effect = is_threepid_reserved
-
     return config