Rename create_test_json_resource to create_test_resource (#8759)

The root resource isn't necessarily a JsonResource, so rename this method
accordingly, and update a couple of test classes to use the method rather than
directly manipulating self.resource.

tests/unittest.py

@@ -30,6 +30,7 @@ from twisted.internet.defer import Deferred, ensureDeferred, succeed
 from twisted.python.failure import Failure
 from twisted.python.threadpool import ThreadPool
 from twisted.trial import unittest
+from twisted.web.resource import Resource
 
 from synapse.api.constants import EventTypes, Membership
 from synapse.config.homeserver import HomeServerConfig
@@ -239,10 +240,8 @@ class HomeserverTestCase(TestCase):
         if not isinstance(self.hs, HomeServer):
             raise Exception("A homeserver wasn't returned, but %r" % (self.hs,))
 
-        # Register the resources
-        self.resource = self.create_test_json_resource()
-
-        # create a site to wrap the resource.
+        # create the root resource, and a site to wrap it.
+        self.resource = self.create_test_resource()
         self.site = SynapseSite(
             logger_name="synapse.access.http.fake",
             site_tag=self.hs.config.server.server_name,
@@ -323,15 +322,12 @@ class HomeserverTestCase(TestCase):
         hs = self.setup_test_homeserver()
         return hs
 
-    def create_test_json_resource(self):
+    def create_test_resource(self) -> Resource:
         """
-        Create a test JsonResource, with the relevant servlets registerd to it
+        Create a the root resource for the test server.
 
-        The default implementation calls each function in `servlets` to do the
-        registration.
-
-        Returns:
-            JsonResource:
+        The default implementation creates a JsonResource and calls each function in
+        `servlets` to register servletes against it
         """
         resource = JsonResource(self.hs)