diff --git a/changelog.d/11880.misc b/changelog.d/11880.misc
new file mode 100644
index 0000000000..8125947b2a
--- /dev/null
+++ b/changelog.d/11880.misc
@@ -0,0 +1 @@
+Convert `ApplicationServiceTestCase` to use `simple_async_mock`.
\ No newline at end of file
diff --git a/tests/appservice/test_appservice.py b/tests/appservice/test_appservice.py
index ba2a2bfd64..07d8105f41 100644
--- a/tests/appservice/test_appservice.py
+++ b/tests/appservice/test_appservice.py
@@ -19,6 +19,7 @@ from twisted.internet import defer
 from synapse.appservice import ApplicationService, Namespace
 
 from tests import unittest
+from tests.test_utils import simple_async_mock
 
 
 def _regex(regex: str, exclusive: bool = True) -> Namespace:
@@ -91,10 +92,10 @@ class ApplicationServiceTestCase(unittest.TestCase):
         self.service.namespaces[ApplicationService.NS_ALIASES].append(
             _regex("#irc_.*:matrix.org")
         )
-        self.store.get_aliases_for_room.return_value = defer.succeed(
+        self.store.get_aliases_for_room = simple_async_mock(
             ["#irc_foobar:matrix.org", "#athing:matrix.org"]
         )
-        self.store.get_users_in_room.return_value = defer.succeed([])
+        self.store.get_users_in_room = simple_async_mock([])
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
@@ -144,10 +145,10 @@ class ApplicationServiceTestCase(unittest.TestCase):
         self.service.namespaces[ApplicationService.NS_ALIASES].append(
             _regex("#irc_.*:matrix.org")
         )
-        self.store.get_aliases_for_room.return_value = defer.succeed(
+        self.store.get_aliases_for_room = simple_async_mock(
             ["#xmpp_foobar:matrix.org", "#athing:matrix.org"]
         )
-        self.store.get_users_in_room.return_value = defer.succeed([])
+        self.store.get_users_in_room = simple_async_mock([])
         self.assertFalse(
             (
                 yield defer.ensureDeferred(
@@ -163,10 +164,8 @@ class ApplicationServiceTestCase(unittest.TestCase):
         )
         self.service.namespaces[ApplicationService.NS_USERS].append(_regex("@irc_.*"))
         self.event.sender = "@irc_foobar:matrix.org"
-        self.store.get_aliases_for_room.return_value = defer.succeed(
-            ["#irc_barfoo:matrix.org"]
-        )
-        self.store.get_users_in_room.return_value = defer.succeed([])
+        self.store.get_aliases_for_room = simple_async_mock(["#irc_barfoo:matrix.org"])
+        self.store.get_users_in_room = simple_async_mock([])
         self.assertTrue(
             (
                 yield defer.ensureDeferred(
@@ -191,10 +190,10 @@ class ApplicationServiceTestCase(unittest.TestCase):
     def test_member_list_match(self):
         self.service.namespaces[ApplicationService.NS_USERS].append(_regex("@irc_.*"))
         # Note that @irc_fo:here is the AS user.
-        self.store.get_users_in_room.return_value = defer.succeed(
+        self.store.get_users_in_room = simple_async_mock(
             ["@alice:here", "@irc_fo:here", "@bob:here"]
         )
-        self.store.get_aliases_for_room.return_value = defer.succeed([])
+        self.store.get_aliases_for_room = simple_async_mock([])
 
         self.event.sender = "@xmpp_foobar:matrix.org"
         self.assertTrue(