Fix test_env in test that re-created it

This particular test restarted the background dispatch service, which
means all receivers were invalidated and had to be recreated.

Using the old receivers caused the test to hang and timeout.. but only
sometimes?

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

tests/test_frequenz_dispatch.py

@@ -426,7 +426,7 @@ async def test_dispatch_new_but_finished(
     generator: DispatchGenerator,
     fake_time: time_machine.Coordinates,
 ) -> None:
-    """Test that a dispatch that is already finished is not started."""
+    """Test that a finished dispatch is not started at startup."""
     # Generate a dispatch that is already finished
     finished_dispatch = generator.generate_dispatch()
     finished_dispatch = replace(
@@ -437,10 +437,25 @@ async def test_dispatch_new_but_finished(
         recurrence=RecurrenceRule(),
         type="TEST_TYPE",
     )
-    # Create an old dispatch
+    # Inject an old dispatch
     test_env.client.set_dispatches(test_env.microgrid_id, [finished_dispatch])
     await test_env.service.stop()
     test_env.service.start()
+    test_env = replace(
+        test_env,
+        lifecycle_events=test_env.service.new_lifecycle_events_receiver("TEST_TYPE"),
+        running_state_change=(
+            await test_env.service.new_running_state_event_receiver(
+                "TEST_TYPE", unify_running_intervals=False
+            )
+        ),
+    )
+
+    fake_time.shift(timedelta(seconds=1))
+    # Process the lifecycle event caused by the old dispatch at startup
+    await test_env.lifecycle_events.receive()
+
+    await asyncio.sleep(1)
 
     # Create another dispatch the normal way
     new_dispatch = generator.generate_dispatch()
@@ -452,8 +467,7 @@ async def test_dispatch_new_but_finished(
         recurrence=RecurrenceRule(),
         type="TEST_TYPE",
     )
-    # Consume one lifecycle_updates event
-    await test_env.lifecycle_events.receive()
+
     new_dispatch = await _test_new_dispatch_created(test_env, new_dispatch)
 
     # Advance time to when the new dispatch should still not start