Add a test of GC on live backends

testbed/tests/test_window.py

@@ -1,5 +1,7 @@
+import gc
 import io
 import traceback
+import weakref
 from importlib import import_module
 from pathlib import Path
 from unittest.mock import Mock
@@ -183,6 +185,32 @@ async def test_secondary_window(app, second_window, second_window_probe):
 
         assert second_window not in app.windows
 
+    async def test_secondary_window_cleanup(app_probe):
+        """Memory for windows is cleaned up when windows are deleted."""
+        # Create and show a window with content. We can't use the second_window fixture
+        # because the fixture will retain a reference, preventing garbage collection.
+        second_window = toga.Window()
+        second_window.content = toga.Box()
+        second_window.show()
+        await app_probe.redraw("Secondary Window has been created")
+
+        # Retain a weak reference to the window to check garbage collection
+        window_ref = weakref.ref(second_window)
+        impl_ref = weakref.ref(second_window._impl)
+
+        second_window.close()
+        await app_probe.redraw("Secondary window has been closed")
+
+        # Clear the local reference to the window (which should be the last reference),
+        # and force a garbage collection pass. This should cause deletion of both the
+        # interface and impl of the window.
+        second_window = None
+        gc.collect()
+
+        # Assert that the weak references are now dead.
+        assert window_ref() is None
+        assert impl_ref() is None
+
     @pytest.mark.parametrize(
         "second_window_kwargs",
         [dict(title="Secondary Window", position=(200, 300), size=(300, 200))],