Refactor homekit_controller config flow tests (#32141)

* Config flow test refactor

* Add a service and characteristic to the accessory so its more realistic

* Feedback from review

* Missing apostrophe

tests/components/homekit_controller/conftest.py

@@ -2,6 +2,8 @@
 import datetime
 from unittest import mock
 
+from aiohomekit.testing import FakeController
+import asynctest
 import pytest
 
 
@@ -12,3 +14,11 @@ def utcnow(request):
     with mock.patch("homeassistant.util.dt.utcnow") as dt_utcnow:
         dt_utcnow.return_value = start_dt
         yield dt_utcnow
+
+
+@pytest.fixture
+def controller(hass):
+    """Replace aiohomekit.Controller with an instance of aiohomekit.testing.FakeController."""
+    instance = FakeController()
+    with asynctest.patch("aiohomekit.Controller", return_value=instance):
+        yield instance