diff --git a/tests/common.py b/tests/common.py
index 88450d34564..38af58642c9 100644
--- a/tests/common.py
+++ b/tests/common.py
@@ -589,12 +589,12 @@ def json_round_trip(obj: Any) -> Any:
 def mock_state_change_event(
     hass: HomeAssistant, new_state: State, old_state: State | None = None
 ) -> None:
-    """Mock state change envent."""
-    event_data = {"entity_id": new_state.entity_id, "new_state": new_state}
-
-    if old_state:
-        event_data["old_state"] = old_state
-
+    """Mock state change event."""
+    event_data = {
+        "entity_id": new_state.entity_id,
+        "new_state": new_state,
+        "old_state": old_state,
+    }
     hass.bus.fire(EVENT_STATE_CHANGED, event_data, context=new_state.context)
 
 
diff --git a/tests/components/mqtt_eventstream/test_init.py b/tests/components/mqtt_eventstream/test_init.py
index 24b4a83c425..90034382fc8 100644
--- a/tests/components/mqtt_eventstream/test_init.py
+++ b/tests/components/mqtt_eventstream/test_init.py
@@ -111,7 +111,7 @@ async def test_state_changed_event_sends_message(
         "last_updated": now.isoformat(),
         "state": "on",
     }
-    event["event_data"] = {"new_state": new_state, "entity_id": e_id}
+    event["event_data"] = {"new_state": new_state, "entity_id": e_id, "old_state": None}
 
     # Verify that the message received was that expected
     result = json.loads(msg)