diff --git a/changelog.d/12066.misc b/changelog.d/12066.misc
new file mode 100644
index 000000000000..0360dbd61edc
--- /dev/null
+++ b/changelog.d/12066.misc
@@ -0,0 +1 @@
+Add type hints to `tests/rest/client`.
diff --git a/tests/rest/client/test_auth.py b/tests/rest/client/test_auth.py
index 4a68d6657321..9653f458379f 100644
--- a/tests/rest/client/test_auth.py
+++ b/tests/rest/client/test_auth.py
@@ -13,17 +13,21 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 from http import HTTPStatus
-from typing import Optional, Tuple, Union
+from typing import Any, Dict, List, Optional, Tuple, Union
 
 from twisted.internet.defer import succeed
+from twisted.test.proto_helpers import MemoryReactor
+from twisted.web.resource import Resource
 
 import synapse.rest.admin
 from synapse.api.constants import LoginType
 from synapse.handlers.ui_auth.checkers import UserInteractiveAuthChecker
 from synapse.rest.client import account, auth, devices, login, logout, register
 from synapse.rest.synapse.client import build_synapse_client_resource_tree
+from synapse.server import HomeServer
 from synapse.storage.database import LoggingTransaction
 from synapse.types import JsonDict, UserID
+from synapse.util import Clock
 
 from tests import unittest
 from tests.handlers.test_oidc import HAS_OIDC
@@ -33,11 +37,11 @@
 
 
 class DummyRecaptchaChecker(UserInteractiveAuthChecker):
-    def __init__(self, hs):
+    def __init__(self, hs: HomeServer) -> None:
         super().__init__(hs)
-        self.recaptcha_attempts = []
+        self.recaptcha_attempts: List[Tuple[dict, str]] = []
 
-    def check_auth(self, authdict, clientip):
+    def check_auth(self, authdict: dict, clientip: str) -> Any:
         self.recaptcha_attempts.append((authdict, clientip))
         return succeed(True)
 
@@ -50,7 +54,7 @@ class FallbackAuthTests(unittest.HomeserverTestCase):
     ]
     hijack_auth = False
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
 
         config = self.default_config()
 
@@ -61,7 +65,7 @@ def make_homeserver(self, reactor, clock):
         hs = self.setup_test_homeserver(config=config)
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.recaptcha_checker = DummyRecaptchaChecker(hs)
         auth_handler = hs.get_auth_handler()
         auth_handler.checkers[LoginType.RECAPTCHA] = self.recaptcha_checker
@@ -101,7 +105,7 @@ def recaptcha(
         self.assertEqual(len(attempts), 1)
         self.assertEqual(attempts[0][0]["response"], "a")
 
-    def test_fallback_captcha(self):
+    def test_fallback_captcha(self) -> None:
         """Ensure that fallback auth via a captcha works."""
         # Returns a 401 as per the spec
         channel = self.register(
@@ -132,7 +136,7 @@ def test_fallback_captcha(self):
         # We're given a registered user.
         self.assertEqual(channel.json_body["user_id"], "@user:test")
 
-    def test_complete_operation_unknown_session(self):
+    def test_complete_operation_unknown_session(self) -> None:
         """
         Attempting to mark an invalid session as complete should error.
         """
@@ -165,7 +169,7 @@ class UIAuthTests(unittest.HomeserverTestCase):
         register.register_servlets,
     ]
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
 
         # public_baseurl uses an http:// scheme because FakeChannel.isSecure() returns
@@ -182,12 +186,12 @@ def default_config(self):
 
         return config
 
-    def create_resource_dict(self):
+    def create_resource_dict(self) -> Dict[str, Resource]:
         resource_dict = super().create_resource_dict()
         resource_dict.update(build_synapse_client_resource_tree(self.hs))
         return resource_dict
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_pass = "pass"
         self.user = self.register_user("test", self.user_pass)
         self.device_id = "dev1"
@@ -229,7 +233,7 @@ def delete_devices(self, expected_response: int, body: JsonDict) -> FakeChannel:
 
         return channel
 
-    def test_ui_auth(self):
+    def test_ui_auth(self) -> None:
         """
         Test user interactive authentication outside of registration.
         """
@@ -259,7 +263,7 @@ def test_ui_auth(self):
             },
         )
 
-    def test_grandfathered_identifier(self):
+    def test_grandfathered_identifier(self) -> None:
         """Check behaviour without "identifier" dict
 
         Synapse used to require clients to submit a "user" field for m.login.password
@@ -286,7 +290,7 @@ def test_grandfathered_identifier(self):
             },
         )
 
-    def test_can_change_body(self):
+    def test_can_change_body(self) -> None:
         """
         The client dict can be modified during the user interactive authentication session.
 
@@ -325,7 +329,7 @@ def test_can_change_body(self):
             },
         )
 
-    def test_cannot_change_uri(self):
+    def test_cannot_change_uri(self) -> None:
         """
         The initial requested URI cannot be modified during the user interactive authentication session.
         """
@@ -362,7 +366,7 @@ def test_cannot_change_uri(self):
         )
 
     @unittest.override_config({"ui_auth": {"session_timeout": "5s"}})
-    def test_can_reuse_session(self):
+    def test_can_reuse_session(self) -> None:
         """
         The session can be reused if configured.
 
@@ -409,7 +413,7 @@ def test_can_reuse_session(self):
 
     @skip_unless(HAS_OIDC, "requires OIDC")
     @override_config({"oidc_config": TEST_OIDC_CONFIG})
-    def test_ui_auth_via_sso(self):
+    def test_ui_auth_via_sso(self) -> None:
         """Test a successful UI Auth flow via SSO
 
         This includes:
@@ -452,7 +456,7 @@ def test_ui_auth_via_sso(self):
 
     @skip_unless(HAS_OIDC, "requires OIDC")
     @override_config({"oidc_config": TEST_OIDC_CONFIG})
-    def test_does_not_offer_password_for_sso_user(self):
+    def test_does_not_offer_password_for_sso_user(self) -> None:
         login_resp = self.helper.login_via_oidc("username")
         user_tok = login_resp["access_token"]
         device_id = login_resp["device_id"]
@@ -464,7 +468,7 @@ def test_does_not_offer_password_for_sso_user(self):
         flows = channel.json_body["flows"]
         self.assertEqual(flows, [{"stages": ["m.login.sso"]}])
 
-    def test_does_not_offer_sso_for_password_user(self):
+    def test_does_not_offer_sso_for_password_user(self) -> None:
         channel = self.delete_device(
             self.user_tok, self.device_id, HTTPStatus.UNAUTHORIZED
         )
@@ -474,7 +478,7 @@ def test_does_not_offer_sso_for_password_user(self):
 
     @skip_unless(HAS_OIDC, "requires OIDC")
     @override_config({"oidc_config": TEST_OIDC_CONFIG})
-    def test_offers_both_flows_for_upgraded_user(self):
+    def test_offers_both_flows_for_upgraded_user(self) -> None:
         """A user that had a password and then logged in with SSO should get both flows"""
         login_resp = self.helper.login_via_oidc(UserID.from_string(self.user).localpart)
         self.assertEqual(login_resp["user_id"], self.user)
@@ -491,7 +495,7 @@ def test_offers_both_flows_for_upgraded_user(self):
 
     @skip_unless(HAS_OIDC, "requires OIDC")
     @override_config({"oidc_config": TEST_OIDC_CONFIG})
-    def test_ui_auth_fails_for_incorrect_sso_user(self):
+    def test_ui_auth_fails_for_incorrect_sso_user(self) -> None:
         """If the user tries to authenticate with the wrong SSO user, they get an error"""
         # log the user in
         login_resp = self.helper.login_via_oidc(UserID.from_string(self.user).localpart)
@@ -534,7 +538,7 @@ class RefreshAuthTests(unittest.HomeserverTestCase):
     ]
     hijack_auth = False
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.user_pass = "pass"
         self.user = self.register_user("test", self.user_pass)
 
@@ -548,7 +552,7 @@ def use_refresh_token(self, refresh_token: str) -> FakeChannel:
             {"refresh_token": refresh_token},
         )
 
-    def is_access_token_valid(self, access_token) -> bool:
+    def is_access_token_valid(self, access_token: str) -> bool:
         """
         Checks whether an access token is valid, returning whether it is or not.
         """
@@ -561,7 +565,7 @@ def is_access_token_valid(self, access_token) -> bool:
 
         return code == HTTPStatus.OK
 
-    def test_login_issue_refresh_token(self):
+    def test_login_issue_refresh_token(self) -> None:
         """
         A login response should include a refresh_token only if asked.
         """
@@ -591,7 +595,7 @@ def test_login_issue_refresh_token(self):
         self.assertIn("refresh_token", login_with_refresh.json_body)
         self.assertIn("expires_in_ms", login_with_refresh.json_body)
 
-    def test_register_issue_refresh_token(self):
+    def test_register_issue_refresh_token(self) -> None:
         """
         A register response should include a refresh_token only if asked.
         """
@@ -627,7 +631,7 @@ def test_register_issue_refresh_token(self):
         self.assertIn("refresh_token", register_with_refresh.json_body)
         self.assertIn("expires_in_ms", register_with_refresh.json_body)
 
-    def test_token_refresh(self):
+    def test_token_refresh(self) -> None:
         """
         A refresh token can be used to issue a new access token.
         """
@@ -665,7 +669,7 @@ def test_token_refresh(self):
         )
 
     @override_config({"refreshable_access_token_lifetime": "1m"})
-    def test_refreshable_access_token_expiration(self):
+    def test_refreshable_access_token_expiration(self) -> None:
         """
         The access token should have some time as specified in the config.
         """
@@ -722,7 +726,9 @@ def test_refreshable_access_token_expiration(self):
             "nonrefreshable_access_token_lifetime": "10m",
         }
     )
-    def test_different_expiry_for_refreshable_and_nonrefreshable_access_tokens(self):
+    def test_different_expiry_for_refreshable_and_nonrefreshable_access_tokens(
+        self,
+    ) -> None:
         """
         Tests that the expiry times for refreshable and non-refreshable access
         tokens can be different.
@@ -782,7 +788,7 @@ def test_different_expiry_for_refreshable_and_nonrefreshable_access_tokens(self)
     @override_config(
         {"refreshable_access_token_lifetime": "1m", "refresh_token_lifetime": "2m"}
     )
-    def test_refresh_token_expiry(self):
+    def test_refresh_token_expiry(self) -> None:
         """
         The refresh token can be configured to have a limited lifetime.
         When that lifetime has ended, the refresh token can no longer be used to
@@ -834,7 +840,7 @@ def test_refresh_token_expiry(self):
             "session_lifetime": "3m",
         }
     )
-    def test_ultimate_session_expiry(self):
+    def test_ultimate_session_expiry(self) -> None:
         """
         The session can be configured to have an ultimate, limited lifetime.
         """
@@ -882,7 +888,7 @@ def test_ultimate_session_expiry(self):
             refresh_response.code, HTTPStatus.FORBIDDEN, refresh_response.result
         )
 
-    def test_refresh_token_invalidation(self):
+    def test_refresh_token_invalidation(self) -> None:
         """Refresh tokens are invalidated after first use of the next token.
 
         A refresh token is considered invalid if:
@@ -987,7 +993,7 @@ def test_refresh_token_invalidation(self):
             fifth_refresh_response.code, HTTPStatus.OK, fifth_refresh_response.result
         )
 
-    def test_many_token_refresh(self):
+    def test_many_token_refresh(self) -> None:
         """
         If a refresh is performed many times during a session, there shouldn't be
         extra 'cruft' built up over time.
diff --git a/tests/rest/client/test_capabilities.py b/tests/rest/client/test_capabilities.py
index 989e80176820..d1751e1557f7 100644
--- a/tests/rest/client/test_capabilities.py
+++ b/tests/rest/client/test_capabilities.py
@@ -13,9 +13,13 @@
 # limitations under the License.
 from http import HTTPStatus
 
+from twisted.test.proto_helpers import MemoryReactor
+
 import synapse.rest.admin
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.rest.client import capabilities, login
+from synapse.server import HomeServer
+from synapse.util import Clock
 
 from tests import unittest
 from tests.unittest import override_config
@@ -29,24 +33,24 @@ class CapabilitiesTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.url = b"/capabilities"
         hs = self.setup_test_homeserver()
         self.config = hs.config
         self.auth_handler = hs.get_auth_handler()
         return hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.localpart = "user"
         self.password = "pass"
         self.user = self.register_user(self.localpart, self.password)
 
-    def test_check_auth_required(self):
+    def test_check_auth_required(self) -> None:
         channel = self.make_request("GET", self.url)
 
         self.assertEqual(channel.code, 401)
 
-    def test_get_room_version_capabilities(self):
+    def test_get_room_version_capabilities(self) -> None:
         access_token = self.login(self.localpart, self.password)
 
         channel = self.make_request("GET", self.url, access_token=access_token)
@@ -61,7 +65,7 @@ def test_get_room_version_capabilities(self):
             capabilities["m.room_versions"]["default"],
         )
 
-    def test_get_change_password_capabilities_password_login(self):
+    def test_get_change_password_capabilities_password_login(self) -> None:
         access_token = self.login(self.localpart, self.password)
 
         channel = self.make_request("GET", self.url, access_token=access_token)
@@ -71,7 +75,7 @@ def test_get_change_password_capabilities_password_login(self):
         self.assertTrue(capabilities["m.change_password"]["enabled"])
 
     @override_config({"password_config": {"localdb_enabled": False}})
-    def test_get_change_password_capabilities_localdb_disabled(self):
+    def test_get_change_password_capabilities_localdb_disabled(self) -> None:
         access_token = self.get_success(
             self.auth_handler.create_access_token_for_user_id(
                 self.user, device_id=None, valid_until_ms=None
@@ -85,7 +89,7 @@ def test_get_change_password_capabilities_localdb_disabled(self):
         self.assertFalse(capabilities["m.change_password"]["enabled"])
 
     @override_config({"password_config": {"enabled": False}})
-    def test_get_change_password_capabilities_password_disabled(self):
+    def test_get_change_password_capabilities_password_disabled(self) -> None:
         access_token = self.get_success(
             self.auth_handler.create_access_token_for_user_id(
                 self.user, device_id=None, valid_until_ms=None
@@ -98,7 +102,7 @@ def test_get_change_password_capabilities_password_disabled(self):
         self.assertEqual(channel.code, 200)
         self.assertFalse(capabilities["m.change_password"]["enabled"])
 
-    def test_get_change_users_attributes_capabilities(self):
+    def test_get_change_users_attributes_capabilities(self) -> None:
         """Test that server returns capabilities by default."""
         access_token = self.login(self.localpart, self.password)
 
@@ -112,7 +116,7 @@ def test_get_change_users_attributes_capabilities(self):
         self.assertTrue(capabilities["m.3pid_changes"]["enabled"])
 
     @override_config({"enable_set_displayname": False})
-    def test_get_set_displayname_capabilities_displayname_disabled(self):
+    def test_get_set_displayname_capabilities_displayname_disabled(self) -> None:
         """Test if set displayname is disabled that the server responds it."""
         access_token = self.login(self.localpart, self.password)
 
@@ -123,7 +127,7 @@ def test_get_set_displayname_capabilities_displayname_disabled(self):
         self.assertFalse(capabilities["m.set_displayname"]["enabled"])
 
     @override_config({"enable_set_avatar_url": False})
-    def test_get_set_avatar_url_capabilities_avatar_url_disabled(self):
+    def test_get_set_avatar_url_capabilities_avatar_url_disabled(self) -> None:
         """Test if set avatar_url is disabled that the server responds it."""
         access_token = self.login(self.localpart, self.password)
 
@@ -134,7 +138,7 @@ def test_get_set_avatar_url_capabilities_avatar_url_disabled(self):
         self.assertFalse(capabilities["m.set_avatar_url"]["enabled"])
 
     @override_config({"enable_3pid_changes": False})
-    def test_get_change_3pid_capabilities_3pid_disabled(self):
+    def test_get_change_3pid_capabilities_3pid_disabled(self) -> None:
         """Test if change 3pid is disabled that the server responds it."""
         access_token = self.login(self.localpart, self.password)
 
@@ -145,7 +149,7 @@ def test_get_change_3pid_capabilities_3pid_disabled(self):
         self.assertFalse(capabilities["m.3pid_changes"]["enabled"])
 
     @override_config({"experimental_features": {"msc3244_enabled": False}})
-    def test_get_does_not_include_msc3244_fields_when_disabled(self):
+    def test_get_does_not_include_msc3244_fields_when_disabled(self) -> None:
         access_token = self.get_success(
             self.auth_handler.create_access_token_for_user_id(
                 self.user, device_id=None, valid_until_ms=None
@@ -160,7 +164,7 @@ def test_get_does_not_include_msc3244_fields_when_disabled(self):
             "org.matrix.msc3244.room_capabilities", capabilities["m.room_versions"]
         )
 
-    def test_get_does_include_msc3244_fields_when_enabled(self):
+    def test_get_does_include_msc3244_fields_when_enabled(self) -> None:
         access_token = self.get_success(
             self.auth_handler.create_access_token_for_user_id(
                 self.user, device_id=None, valid_until_ms=None
diff --git a/tests/rest/client/test_login.py b/tests/rest/client/test_login.py
index 26d0d83e00f2..d48defda6386 100644
--- a/tests/rest/client/test_login.py
+++ b/tests/rest/client/test_login.py
@@ -20,6 +20,7 @@
 
 import pymacaroons
 
+from twisted.test.proto_helpers import MemoryReactor
 from twisted.web.resource import Resource
 
 import synapse.rest.admin
@@ -27,12 +28,15 @@
 from synapse.rest.client import devices, login, logout, register
 from synapse.rest.client.account import WhoamiRestServlet
 from synapse.rest.synapse.client import build_synapse_client_resource_tree
+from synapse.server import HomeServer
 from synapse.types import create_requester
+from synapse.util import Clock
 
 from tests import unittest
 from tests.handlers.test_oidc import HAS_OIDC
 from tests.handlers.test_saml import has_saml2
 from tests.rest.client.utils import TEST_OIDC_AUTH_ENDPOINT, TEST_OIDC_CONFIG
+from tests.server import FakeChannel
 from tests.test_utils.html_parsers import TestHtmlParser
 from tests.unittest import HomeserverTestCase, override_config, skip_unless
 
@@ -95,7 +99,7 @@ class LoginRestServletTestCase(unittest.HomeserverTestCase):
         lambda hs, http_server: WhoamiRestServlet(hs).register(http_server),
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.hs = self.setup_test_homeserver()
         self.hs.config.registration.enable_registration = True
         self.hs.config.registration.registrations_require_3pid = []
@@ -117,7 +121,7 @@ def make_homeserver(self, reactor, clock):
             }
         }
     )
-    def test_POST_ratelimiting_per_address(self):
+    def test_POST_ratelimiting_per_address(self) -> None:
         # Create different users so we're sure not to be bothered by the per-user
         # ratelimiter.
         for i in range(0, 6):
@@ -165,7 +169,7 @@ def test_POST_ratelimiting_per_address(self):
             }
         }
     )
-    def test_POST_ratelimiting_per_account(self):
+    def test_POST_ratelimiting_per_account(self) -> None:
         self.register_user("kermit", "monkey")
 
         for i in range(0, 6):
@@ -210,7 +214,7 @@ def test_POST_ratelimiting_per_account(self):
             }
         }
     )
-    def test_POST_ratelimiting_per_account_failed_attempts(self):
+    def test_POST_ratelimiting_per_account_failed_attempts(self) -> None:
         self.register_user("kermit", "monkey")
 
         for i in range(0, 6):
@@ -243,7 +247,7 @@ def test_POST_ratelimiting_per_account_failed_attempts(self):
         self.assertEquals(channel.result["code"], b"403", channel.result)
 
     @override_config({"session_lifetime": "24h"})
-    def test_soft_logout(self):
+    def test_soft_logout(self) -> None:
         self.register_user("kermit", "monkey")
 
         # we shouldn't be able to make requests without an access token
@@ -298,7 +302,9 @@ def test_soft_logout(self):
         self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
         self.assertEquals(channel.json_body["soft_logout"], False)
 
-    def _delete_device(self, access_token, user_id, password, device_id):
+    def _delete_device(
+        self, access_token: str, user_id: str, password: str, device_id: str
+    ) -> None:
         """Perform the UI-Auth to delete a device"""
         channel = self.make_request(
             b"DELETE", "devices/" + device_id, access_token=access_token
@@ -329,7 +335,7 @@ def _delete_device(self, access_token, user_id, password, device_id):
         self.assertEquals(channel.code, 200, channel.result)
 
     @override_config({"session_lifetime": "24h"})
-    def test_session_can_hard_logout_after_being_soft_logged_out(self):
+    def test_session_can_hard_logout_after_being_soft_logged_out(self) -> None:
         self.register_user("kermit", "monkey")
 
         # log in as normal
@@ -353,7 +359,9 @@ def test_session_can_hard_logout_after_being_soft_logged_out(self):
         self.assertEquals(channel.result["code"], b"200", channel.result)
 
     @override_config({"session_lifetime": "24h"})
-    def test_session_can_hard_logout_all_sessions_after_being_soft_logged_out(self):
+    def test_session_can_hard_logout_all_sessions_after_being_soft_logged_out(
+        self,
+    ) -> None:
         self.register_user("kermit", "monkey")
 
         # log in as normal
@@ -432,7 +440,7 @@ def create_resource_dict(self) -> Dict[str, Resource]:
         d.update(build_synapse_client_resource_tree(self.hs))
         return d
 
-    def test_get_login_flows(self):
+    def test_get_login_flows(self) -> None:
         """GET /login should return password and SSO flows"""
         channel = self.make_request("GET", "/_matrix/client/r0/login")
         self.assertEqual(channel.code, 200, channel.result)
@@ -459,12 +467,14 @@ def test_get_login_flows(self):
             ],
         )
 
-    def test_multi_sso_redirect(self):
+    def test_multi_sso_redirect(self) -> None:
         """/login/sso/redirect should redirect to an identity picker"""
         # first hit the redirect url, which should redirect to our idp picker
         channel = self._make_sso_redirect_request(None)
         self.assertEqual(channel.code, 302, channel.result)
-        uri = channel.headers.getRawHeaders("Location")[0]
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        uri = location_headers[0]
 
         # hitting that picker should give us some HTML
         channel = self.make_request("GET", uri)
@@ -487,7 +497,7 @@ def test_multi_sso_redirect(self):
 
         self.assertCountEqual(returned_idps, ["cas", "oidc", "oidc-idp1", "saml"])
 
-    def test_multi_sso_redirect_to_cas(self):
+    def test_multi_sso_redirect_to_cas(self) -> None:
         """If CAS is chosen, should redirect to the CAS server"""
 
         channel = self.make_request(
@@ -514,7 +524,7 @@ def test_multi_sso_redirect_to_cas(self):
         service_uri_params = urllib.parse.parse_qs(service_uri_query)
         self.assertEqual(service_uri_params["redirectUrl"][0], TEST_CLIENT_REDIRECT_URL)
 
-    def test_multi_sso_redirect_to_saml(self):
+    def test_multi_sso_redirect_to_saml(self) -> None:
         """If SAML is chosen, should redirect to the SAML server"""
         channel = self.make_request(
             "GET",
@@ -536,7 +546,7 @@ def test_multi_sso_redirect_to_saml(self):
         relay_state_param = saml_uri_params["RelayState"][0]
         self.assertEqual(relay_state_param, TEST_CLIENT_REDIRECT_URL)
 
-    def test_login_via_oidc(self):
+    def test_login_via_oidc(self) -> None:
         """If OIDC is chosen, should redirect to the OIDC auth endpoint"""
 
         # pick the default OIDC provider
@@ -604,7 +614,7 @@ def test_login_via_oidc(self):
         self.assertEqual(chan.code, 200, chan.result)
         self.assertEqual(chan.json_body["user_id"], "@user1:test")
 
-    def test_multi_sso_redirect_to_unknown(self):
+    def test_multi_sso_redirect_to_unknown(self) -> None:
         """An unknown IdP should cause a 400"""
         channel = self.make_request(
             "GET",
@@ -612,23 +622,25 @@ def test_multi_sso_redirect_to_unknown(self):
         )
         self.assertEqual(channel.code, 400, channel.result)
 
-    def test_client_idp_redirect_to_unknown(self):
+    def test_client_idp_redirect_to_unknown(self) -> None:
         """If the client tries to pick an unknown IdP, return a 404"""
         channel = self._make_sso_redirect_request("xxx")
         self.assertEqual(channel.code, 404, channel.result)
         self.assertEqual(channel.json_body["errcode"], "M_NOT_FOUND")
 
-    def test_client_idp_redirect_to_oidc(self):
+    def test_client_idp_redirect_to_oidc(self) -> None:
         """If the client pick a known IdP, redirect to it"""
         channel = self._make_sso_redirect_request("oidc")
         self.assertEqual(channel.code, 302, channel.result)
-        oidc_uri = channel.headers.getRawHeaders("Location")[0]
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        oidc_uri = location_headers[0]
         oidc_uri_path, oidc_uri_query = oidc_uri.split("?", 1)
 
         # it should redirect us to the auth page of the OIDC server
         self.assertEqual(oidc_uri_path, TEST_OIDC_AUTH_ENDPOINT)
 
-    def _make_sso_redirect_request(self, idp_prov: Optional[str] = None):
+    def _make_sso_redirect_request(self, idp_prov: Optional[str] = None) -> FakeChannel:
         """Send a request to /_matrix/client/r0/login/sso/redirect
 
         ... possibly specifying an IDP provider
@@ -659,7 +671,7 @@ class CASTestCase(unittest.HomeserverTestCase):
         login.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.base_url = "https://matrix.goodserver.com/"
         self.redirect_path = "_synapse/client/login/sso/redirect/confirm"
 
@@ -675,7 +687,7 @@ def make_homeserver(self, reactor, clock):
         cas_user_id = "username"
         self.user_id = "@%s:test" % cas_user_id
 
-        async def get_raw(uri, args):
+        async def get_raw(uri: str, args: Any) -> bytes:
             """Return an example response payload from a call to the `/proxyValidate`
             endpoint of a CAS server, copied from
             https://apereo.github.io/cas/5.0.x/protocol/CAS-Protocol-V2-Specification.html#26-proxyvalidate-cas-20
@@ -709,10 +721,10 @@ async def get_raw(uri, args):
 
         return self.hs
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.deactivate_account_handler = hs.get_deactivate_account_handler()
 
-    def test_cas_redirect_confirm(self):
+    def test_cas_redirect_confirm(self) -> None:
         """Tests that the SSO login flow serves a confirmation page before redirecting a
         user to the redirect URL.
         """
@@ -754,15 +766,15 @@ def test_cas_redirect_confirm(self):
             }
         }
     )
-    def test_cas_redirect_whitelisted(self):
+    def test_cas_redirect_whitelisted(self) -> None:
         """Tests that the SSO login flow serves a redirect to a whitelisted url"""
         self._test_redirect("https://legit-site.com/")
 
     @override_config({"public_baseurl": "https://example.com"})
-    def test_cas_redirect_login_fallback(self):
+    def test_cas_redirect_login_fallback(self) -> None:
         self._test_redirect("https://example.com/_matrix/static/client/login")
 
-    def _test_redirect(self, redirect_url):
+    def _test_redirect(self, redirect_url: str) -> None:
         """Tests that the SSO login flow serves a redirect for the given redirect URL."""
         cas_ticket_url = (
             "/_matrix/client/r0/login/cas/ticket?redirectUrl=%s&ticket=ticket"
@@ -778,7 +790,7 @@ def _test_redirect(self, redirect_url):
         self.assertEqual(location_headers[0][: len(redirect_url)], redirect_url)
 
     @override_config({"sso": {"client_whitelist": ["https://legit-site.com/"]}})
-    def test_deactivated_user(self):
+    def test_deactivated_user(self) -> None:
         """Logging in as a deactivated account should error."""
         redirect_url = "https://legit-site.com/"
 
@@ -821,7 +833,7 @@ class JWTTestCase(unittest.HomeserverTestCase):
         "algorithm": jwt_algorithm,
     }
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
 
         # If jwt_config has been defined (eg via @override_config), don't replace it.
@@ -837,23 +849,23 @@ def jwt_encode(self, payload: Dict[str, Any], secret: str = jwt_secret) -> str:
             return result.decode("ascii")
         return result
 
-    def jwt_login(self, *args):
+    def jwt_login(self, *args: Any) -> FakeChannel:
         params = {"type": "org.matrix.login.jwt", "token": self.jwt_encode(*args)}
         channel = self.make_request(b"POST", LOGIN_URL, params)
         return channel
 
-    def test_login_jwt_valid_registered(self):
+    def test_login_jwt_valid_registered(self) -> None:
         self.register_user("kermit", "monkey")
         channel = self.jwt_login({"sub": "kermit"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@kermit:test")
 
-    def test_login_jwt_valid_unregistered(self):
+    def test_login_jwt_valid_unregistered(self) -> None:
         channel = self.jwt_login({"sub": "frog"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@frog:test")
 
-    def test_login_jwt_invalid_signature(self):
+    def test_login_jwt_invalid_signature(self) -> None:
         channel = self.jwt_login({"sub": "frog"}, "notsecret")
         self.assertEqual(channel.result["code"], b"403", channel.result)
         self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
@@ -862,7 +874,7 @@ def test_login_jwt_invalid_signature(self):
             "JWT validation failed: Signature verification failed",
         )
 
-    def test_login_jwt_expired(self):
+    def test_login_jwt_expired(self) -> None:
         channel = self.jwt_login({"sub": "frog", "exp": 864000})
         self.assertEqual(channel.result["code"], b"403", channel.result)
         self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
@@ -870,7 +882,7 @@ def test_login_jwt_expired(self):
             channel.json_body["error"], "JWT validation failed: Signature has expired"
         )
 
-    def test_login_jwt_not_before(self):
+    def test_login_jwt_not_before(self) -> None:
         now = int(time.time())
         channel = self.jwt_login({"sub": "frog", "nbf": now + 3600})
         self.assertEqual(channel.result["code"], b"403", channel.result)
@@ -880,14 +892,14 @@ def test_login_jwt_not_before(self):
             "JWT validation failed: The token is not yet valid (nbf)",
         )
 
-    def test_login_no_sub(self):
+    def test_login_no_sub(self) -> None:
         channel = self.jwt_login({"username": "root"})
         self.assertEqual(channel.result["code"], b"403", channel.result)
         self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
         self.assertEqual(channel.json_body["error"], "Invalid JWT")
 
     @override_config({"jwt_config": {**base_config, "issuer": "test-issuer"}})
-    def test_login_iss(self):
+    def test_login_iss(self) -> None:
         """Test validating the issuer claim."""
         # A valid issuer.
         channel = self.jwt_login({"sub": "kermit", "iss": "test-issuer"})
@@ -911,14 +923,14 @@ def test_login_iss(self):
             'JWT validation failed: Token is missing the "iss" claim',
         )
 
-    def test_login_iss_no_config(self):
+    def test_login_iss_no_config(self) -> None:
         """Test providing an issuer claim without requiring it in the configuration."""
         channel = self.jwt_login({"sub": "kermit", "iss": "invalid"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@kermit:test")
 
     @override_config({"jwt_config": {**base_config, "audiences": ["test-audience"]}})
-    def test_login_aud(self):
+    def test_login_aud(self) -> None:
         """Test validating the audience claim."""
         # A valid audience.
         channel = self.jwt_login({"sub": "kermit", "aud": "test-audience"})
@@ -942,7 +954,7 @@ def test_login_aud(self):
             'JWT validation failed: Token is missing the "aud" claim',
         )
 
-    def test_login_aud_no_config(self):
+    def test_login_aud_no_config(self) -> None:
         """Test providing an audience without requiring it in the configuration."""
         channel = self.jwt_login({"sub": "kermit", "aud": "invalid"})
         self.assertEqual(channel.result["code"], b"403", channel.result)
@@ -951,20 +963,20 @@ def test_login_aud_no_config(self):
             channel.json_body["error"], "JWT validation failed: Invalid audience"
         )
 
-    def test_login_default_sub(self):
+    def test_login_default_sub(self) -> None:
         """Test reading user ID from the default subject claim."""
         channel = self.jwt_login({"sub": "kermit"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@kermit:test")
 
     @override_config({"jwt_config": {**base_config, "subject_claim": "username"}})
-    def test_login_custom_sub(self):
+    def test_login_custom_sub(self) -> None:
         """Test reading user ID from a custom subject claim."""
         channel = self.jwt_login({"username": "frog"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@frog:test")
 
-    def test_login_no_token(self):
+    def test_login_no_token(self) -> None:
         params = {"type": "org.matrix.login.jwt"}
         channel = self.make_request(b"POST", LOGIN_URL, params)
         self.assertEqual(channel.result["code"], b"403", channel.result)
@@ -1026,7 +1038,7 @@ class JWTPubKeyTestCase(unittest.HomeserverTestCase):
         ]
     )
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
         config["jwt_config"] = {
             "enabled": True,
@@ -1042,17 +1054,17 @@ def jwt_encode(self, payload: Dict[str, Any], secret: str = jwt_privatekey) -> s
             return result.decode("ascii")
         return result
 
-    def jwt_login(self, *args):
+    def jwt_login(self, *args: Any) -> FakeChannel:
         params = {"type": "org.matrix.login.jwt", "token": self.jwt_encode(*args)}
         channel = self.make_request(b"POST", LOGIN_URL, params)
         return channel
 
-    def test_login_jwt_valid(self):
+    def test_login_jwt_valid(self) -> None:
         channel = self.jwt_login({"sub": "kermit"})
         self.assertEqual(channel.result["code"], b"200", channel.result)
         self.assertEqual(channel.json_body["user_id"], "@kermit:test")
 
-    def test_login_jwt_invalid_signature(self):
+    def test_login_jwt_invalid_signature(self) -> None:
         channel = self.jwt_login({"sub": "frog"}, self.bad_privatekey)
         self.assertEqual(channel.result["code"], b"403", channel.result)
         self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
@@ -1071,7 +1083,7 @@ class AppserviceLoginRestServletTestCase(unittest.HomeserverTestCase):
         register.register_servlets,
     ]
 
-    def make_homeserver(self, reactor, clock):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
         self.hs = self.setup_test_homeserver()
 
         self.service = ApplicationService(
@@ -1105,7 +1117,7 @@ def make_homeserver(self, reactor, clock):
         self.hs.get_datastores().main.services_cache.append(self.another_service)
         return self.hs
 
-    def test_login_appservice_user(self):
+    def test_login_appservice_user(self) -> None:
         """Test that an appservice user can use /login"""
         self.register_appservice_user(AS_USER, self.service.token)
 
@@ -1119,7 +1131,7 @@ def test_login_appservice_user(self):
 
         self.assertEquals(channel.result["code"], b"200", channel.result)
 
-    def test_login_appservice_user_bot(self):
+    def test_login_appservice_user_bot(self) -> None:
         """Test that the appservice bot can use /login"""
         self.register_appservice_user(AS_USER, self.service.token)
 
@@ -1133,7 +1145,7 @@ def test_login_appservice_user_bot(self):
 
         self.assertEquals(channel.result["code"], b"200", channel.result)
 
-    def test_login_appservice_wrong_user(self):
+    def test_login_appservice_wrong_user(self) -> None:
         """Test that non-as users cannot login with the as token"""
         self.register_appservice_user(AS_USER, self.service.token)
 
@@ -1147,7 +1159,7 @@ def test_login_appservice_wrong_user(self):
 
         self.assertEquals(channel.result["code"], b"403", channel.result)
 
-    def test_login_appservice_wrong_as(self):
+    def test_login_appservice_wrong_as(self) -> None:
         """Test that as users cannot login with wrong as token"""
         self.register_appservice_user(AS_USER, self.service.token)
 
@@ -1161,7 +1173,7 @@ def test_login_appservice_wrong_as(self):
 
         self.assertEquals(channel.result["code"], b"403", channel.result)
 
-    def test_login_appservice_no_token(self):
+    def test_login_appservice_no_token(self) -> None:
         """Test that users must provide a token when using the appservice
         login method
         """
@@ -1182,7 +1194,7 @@ class UsernamePickerTestCase(HomeserverTestCase):
 
     servlets = [login.register_servlets]
 
-    def default_config(self):
+    def default_config(self) -> Dict[str, Any]:
         config = super().default_config()
         config["public_baseurl"] = BASE_URL
 
@@ -1202,7 +1214,7 @@ def create_resource_dict(self) -> Dict[str, Resource]:
         d.update(build_synapse_client_resource_tree(self.hs))
         return d
 
-    def test_username_picker(self):
+    def test_username_picker(self) -> None:
         """Test the happy path of a username picker flow."""
 
         # do the start of the login flow
diff --git a/tests/rest/client/test_sync.py b/tests/rest/client/test_sync.py
index e06256136548..69b4ef537843 100644
--- a/tests/rest/client/test_sync.py
+++ b/tests/rest/client/test_sync.py
@@ -13,9 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import json
+from typing import List, Optional
 
 from parameterized import parameterized
 
+from twisted.test.proto_helpers import MemoryReactor
+
 import synapse.rest.admin
 from synapse.api.constants import (
     EventContentFields,
@@ -24,6 +27,9 @@
     RelationTypes,
 )
 from synapse.rest.client import devices, knock, login, read_marker, receipts, room, sync
+from synapse.server import HomeServer
+from synapse.types import JsonDict
+from synapse.util import Clock
 
 from tests import unittest
 from tests.federation.transport.test_knocking import (
@@ -43,7 +49,7 @@ class FilterTestCase(unittest.HomeserverTestCase):
         sync.register_servlets,
     ]
 
-    def test_sync_argless(self):
+    def test_sync_argless(self) -> None:
         channel = self.make_request("GET", "/sync")
 
         self.assertEqual(channel.code, 200)
@@ -58,7 +64,7 @@ class SyncFilterTestCase(unittest.HomeserverTestCase):
         sync.register_servlets,
     ]
 
-    def test_sync_filter_labels(self):
+    def test_sync_filter_labels(self) -> None:
         """Test that we can filter by a label."""
         sync_filter = json.dumps(
             {
@@ -77,7 +83,7 @@ def test_sync_filter_labels(self):
         self.assertEqual(events[0]["content"]["body"], "with right label", events[0])
         self.assertEqual(events[1]["content"]["body"], "with right label", events[1])
 
-    def test_sync_filter_not_labels(self):
+    def test_sync_filter_not_labels(self) -> None:
         """Test that we can filter by the absence of a label."""
         sync_filter = json.dumps(
             {
@@ -99,7 +105,7 @@ def test_sync_filter_not_labels(self):
             events[2]["content"]["body"], "with two wrong labels", events[2]
         )
 
-    def test_sync_filter_labels_not_labels(self):
+    def test_sync_filter_labels_not_labels(self) -> None:
         """Test that we can filter by both a label and the absence of another label."""
         sync_filter = json.dumps(
             {
@@ -118,7 +124,7 @@ def test_sync_filter_labels_not_labels(self):
         self.assertEqual(len(events), 1, [event["content"] for event in events])
         self.assertEqual(events[0]["content"]["body"], "with wrong label", events[0])
 
-    def _test_sync_filter_labels(self, sync_filter):
+    def _test_sync_filter_labels(self, sync_filter: str) -> List[JsonDict]:
         user_id = self.register_user("kermit", "test")
         tok = self.login("kermit", "test")
 
@@ -194,7 +200,7 @@ class SyncTypingTests(unittest.HomeserverTestCase):
     user_id = True
     hijack_auth = False
 
-    def test_sync_backwards_typing(self):
+    def test_sync_backwards_typing(self) -> None:
         """
         If the typing serial goes backwards and the typing handler is then reset
         (such as when the master restarts and sets the typing serial to 0), we
@@ -298,7 +304,7 @@ class SyncKnockTestCase(
         knock.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.store = hs.get_datastores().main
         self.url = "/sync?since=%s"
         self.next_batch = "s0"
@@ -336,7 +342,7 @@ def prepare(self, reactor, clock, hs):
         )
 
     @override_config({"experimental_features": {"msc2403_enabled": True}})
-    def test_knock_room_state(self):
+    def test_knock_room_state(self) -> None:
         """Tests that /sync returns state from a room after knocking on it."""
         # Knock on a room
         channel = self.make_request(
@@ -383,7 +389,7 @@ class ReadReceiptsTestCase(unittest.HomeserverTestCase):
         sync.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.url = "/sync?since=%s"
         self.next_batch = "s0"
 
@@ -402,7 +408,7 @@ def prepare(self, reactor, clock, hs):
         self.helper.join(room=self.room_id, user=self.user2, tok=self.tok2)
 
     @override_config({"experimental_features": {"msc2285_enabled": True}})
-    def test_hidden_read_receipts(self):
+    def test_hidden_read_receipts(self) -> None:
         # Send a message as the first user
         res = self.helper.send(self.room_id, body="hello", tok=self.tok)
 
@@ -441,8 +447,8 @@ def test_hidden_read_receipts(self):
         ]
     )
     def test_read_receipt_with_empty_body(
-        self, name, user_agent: str, expected_status_code: int
-    ):
+        self, name: str, user_agent: str, expected_status_code: int
+    ) -> None:
         # Send a message as the first user
         res = self.helper.send(self.room_id, body="hello", tok=self.tok)
 
@@ -455,11 +461,11 @@ def test_read_receipt_with_empty_body(
         )
         self.assertEqual(channel.code, expected_status_code)
 
-    def _get_read_receipt(self):
+    def _get_read_receipt(self) -> Optional[JsonDict]:
         """Syncs and returns the read receipt."""
 
         # Checks if event is a read receipt
-        def is_read_receipt(event):
+        def is_read_receipt(event: JsonDict) -> bool:
             return event["type"] == "m.receipt"
 
         # Sync
@@ -477,7 +483,8 @@ def is_read_receipt(event):
         ephemeral_events = channel.json_body["rooms"]["join"][self.room_id][
             "ephemeral"
         ]["events"]
-        return next(filter(is_read_receipt, ephemeral_events), None)
+        receipt_event = filter(is_read_receipt, ephemeral_events)
+        return next(receipt_event, None)
 
 
 class UnreadMessagesTestCase(unittest.HomeserverTestCase):
@@ -490,7 +497,7 @@ class UnreadMessagesTestCase(unittest.HomeserverTestCase):
         receipts.register_servlets,
     ]
 
-    def prepare(self, reactor, clock, hs):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
         self.url = "/sync?since=%s"
         self.next_batch = "s0"
 
@@ -533,7 +540,7 @@ def prepare(self, reactor, clock, hs):
             tok=self.tok,
         )
 
-    def test_unread_counts(self):
+    def test_unread_counts(self) -> None:
         """Tests that /sync returns the right value for the unread count (MSC2654)."""
 
         # Check that our own messages don't increase the unread count.
@@ -640,7 +647,7 @@ def test_unread_counts(self):
         )
         self._check_unread_count(5)
 
-    def _check_unread_count(self, expected_count: int):
+    def _check_unread_count(self, expected_count: int) -> None:
         """Syncs and compares the unread count with the expected value."""
 
         channel = self.make_request(
@@ -669,7 +676,7 @@ class SyncCacheTestCase(unittest.HomeserverTestCase):
         sync.register_servlets,
     ]
 
-    def test_noop_sync_does_not_tightloop(self):
+    def test_noop_sync_does_not_tightloop(self) -> None:
         """If the sync times out, we shouldn't cache the result
 
         Essentially a regression test for #8518.
@@ -720,7 +727,7 @@ class DeviceListSyncTestCase(unittest.HomeserverTestCase):
         devices.register_servlets,
     ]
 
-    def test_user_with_no_rooms_receives_self_device_list_updates(self):
+    def test_user_with_no_rooms_receives_self_device_list_updates(self) -> None:
         """Tests that a user with no rooms still receives their own device list updates"""
         device_id = "TESTDEVICE"