add test

tests/test_screens.py

@@ -11,6 +11,22 @@ skip_py310 = pytest.mark.skipif(
 )
 
 
+async def test_screen_walk_children():
+    """Test query only reports active screen."""
+
+    class ScreensApp(App):
+        pass
+
+    app = ScreensApp()
+    async with app.run_test() as pilot:
+        screen1 = Screen()
+        screen2 = Screen()
+        pilot.app.push_screen(screen1)
+        assert list(pilot.app.query("*")) == [screen1]
+        pilot.app.push_screen(screen2)
+        assert list(pilot.app.query("*")) == [screen2]
+
+
 async def test_installed_screens():
     class ScreensApp(App):
         SCREENS = {