comment on test

tests/test_app.py

@@ -2,11 +2,16 @@ from textual.app import App
 
 
 def test_batch_update():
+    """Test `batch_update` context manager"""
     app = App()
-    assert app._batch_count == 0
+    assert app._batch_count == 0  # Start at zero
+
     with app.batch_update():
-        assert app._batch_count == 1
+        assert app._batch_count == 1  # Increments in context manager
+
         with app.batch_update():
-            assert app._batch_count == 2
-        assert app._batch_count == 1
-    assert app._batch_count == 0
+            assert app._batch_count == 2  # Nested updates
+
+        assert app._batch_count == 1  # Exiting decrements
+
+    assert app._batch_count == 0  # Back to zero