diff --git a/changelog.d/13809.misc b/changelog.d/13809.misc
new file mode 100644
index 0000000000..c2dacca2f2
--- /dev/null
+++ b/changelog.d/13809.misc
@@ -0,0 +1 @@
+Improve the `synapse.api.auth.Auth` mock used in unit tests.
diff --git a/tests/unittest.py b/tests/unittest.py
index 975b0a23a7..00cb023198 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -300,47 +300,31 @@ class HomeserverTestCase(TestCase):
         if hasattr(self, "user_id"):
             if self.hijack_auth:
                 assert self.helper.auth_user_id is not None
+                token = "some_fake_token"
 
                 # We need a valid token ID to satisfy foreign key constraints.
                 token_id = self.get_success(
                     self.hs.get_datastores().main.add_access_token_to_user(
                         self.helper.auth_user_id,
-                        "some_fake_token",
+                        token,
                         None,
                         None,
                     )
                 )
 
-                async def get_user_by_access_token(
-                    token: Optional[str] = None, allow_guest: bool = False
-                ) -> JsonDict:
-                    assert self.helper.auth_user_id is not None
-                    return {
-                        "user": UserID.from_string(self.helper.auth_user_id),
-                        "token_id": token_id,
-                        "is_guest": False,
-                    }
-
-                async def get_user_by_req(
-                    request: SynapseRequest,
-                    allow_guest: bool = False,
-                    allow_expired: bool = False,
-                ) -> Requester:
+                # This has to be a function and not just a Mock, because
+                # `self.helper.auth_user_id` is temporarily reassigned in some tests
+                async def get_requester(*args, **kwargs) -> Requester:
                     assert self.helper.auth_user_id is not None
                     return create_requester(
-                        UserID.from_string(self.helper.auth_user_id),
-                        token_id,
-                        False,
-                        False,
-                        None,
+                        user_id=UserID.from_string(self.helper.auth_user_id),
+                        access_token_id=token_id,
                     )
 
                 # Type ignore: mypy doesn't like us assigning to methods.
-                self.hs.get_auth().get_user_by_req = get_user_by_req  # type: ignore[assignment]
-                self.hs.get_auth().get_user_by_access_token = get_user_by_access_token  # type: ignore[assignment]
-                self.hs.get_auth().get_access_token_from_request = Mock(  # type: ignore[assignment]
-                    return_value="1234"
-                )
+                self.hs.get_auth().get_user_by_req = get_requester  # type: ignore[assignment]
+                self.hs.get_auth().get_user_by_access_token = get_requester  # type: ignore[assignment]
+                self.hs.get_auth().get_access_token_from_request = Mock(return_value=token)  # type: ignore[assignment]
 
         if self.needs_threadpool:
             self.reactor.threadpool = ThreadPool()  # type: ignore[assignment]