Ensure proper cleanup and error handling in test fixtures (zauberzeug#5287)

### Motivation

If an exception happens inside the fixture setup, the fixture was not
reset correctly leading to failed tests.

### Implementation

- Updated `screen` and `user` fixtures to use `try...finally` for
resource cleanup, ensuring environment variables are reset and servers
are stopped even if an error occurs.
- Improved error logging by checking for unexpected ERROR logs after
yielding the fixture.
- reactivate tests from `test_main_file_marker.py` (which failed before)

This change enhances the reliability of the testing framework by
ensuring that resources are properly managed and that errors are logged
appropriately.


### Progress

- [x] I chose a meaningful title that completes the sentence: "If
applied, this PR will..."
- [x] The implementation is complete.
- [x] Pytests have been reactivated.
- [x] Documentation is not necessary.

Author: rodja

nicegui/testing/screen_plugin.py

@@ -82,14 +82,17 @@ def screen(nicegui_reset_globals,  # noqa: F811, pylint: disable=unused-argument
     """Create a new SeleniumScreen fixture."""
     os.environ['NICEGUI_SCREEN_TEST_PORT'] = str(Screen.PORT)
     screen_ = Screen(nicegui_driver, caplog, request)
-    yield screen_
-    os.environ.pop('NICEGUI_SCREEN_TEST_PORT', None)
-    logs = [record for record in screen_.caplog.get_records('call') if record.levelname == 'ERROR']
-    if screen_.is_open:
-        test_failed = hasattr(request.node, 'rep_call') and request.node.rep_call.failed
-        screen_.shot(request.node.name, failed=test_failed or bool(logs))
-    screen_.stop_server()
-    if DOWNLOAD_DIR.exists():
-        shutil.rmtree(DOWNLOAD_DIR)
-    if logs:
-        pytest.fail('There were unexpected ERROR logs.', pytrace=False)
+    try:
+        yield screen_
+
+        logs = [record for record in screen_.caplog.get_records('call') if record.levelname == 'ERROR']
+        if screen_.is_open:
+            test_failed = hasattr(request.node, 'rep_call') and request.node.rep_call.failed
+            screen_.shot(request.node.name, failed=test_failed or bool(logs))
+        if logs:
+            pytest.fail('There were unexpected ERROR logs.', pytrace=False)
+    finally:
+        os.environ.pop('NICEGUI_SCREEN_TEST_PORT', None)
+        screen_.stop_server()
+        if DOWNLOAD_DIR.exists():
+            shutil.rmtree(DOWNLOAD_DIR)

nicegui/testing/user_plugin.py

@@ -30,33 +30,36 @@ async def user(nicegui_reset_globals,  # noqa: F811, pylint: disable=unused-argu
                ) -> AsyncGenerator[User, None]:
     """Create a new user fixture."""
     os.environ['NICEGUI_USER_SIMULATION'] = 'true'
-    main_path = get_path_to_main_file(request)
-    if main_path is None:
-        prepare_simulation()
-        ui.run(storage_secret='simulated secret')
-    else:
-        runpy.run_path(str(main_path), run_name='__main__')
+    try:
+        main_path = get_path_to_main_file(request)
+        if main_path is None:
+            prepare_simulation()
+            ui.run(storage_secret='simulated secret')
+        else:
+            runpy.run_path(str(main_path), run_name='__main__')
 
-    async with core.app.router.lifespan_context(core.app):
-        async with httpx.AsyncClient(transport=httpx.ASGITransport(core.app), base_url='http://test') as client:
-            yield User(client)
+        async with core.app.router.lifespan_context(core.app):
+            async with httpx.AsyncClient(transport=httpx.ASGITransport(core.app), base_url='http://test') as client:
+                yield User(client)
 
-    os.environ.pop('NICEGUI_USER_SIMULATION', None)
-    ui.navigate = Navigate()
-    ui.notify = notify
-    ui.download = download
-
-    logs = [record for record in caplog.get_records('call') if record.levelname == 'ERROR']
-    if logs:
-        pytest.fail('There were unexpected ERROR logs.', pytrace=False)
+        logs = [record for record in caplog.get_records('call') if record.levelname == 'ERROR']
+        if logs:
+            pytest.fail('There were unexpected ERROR logs.', pytrace=False)
+    finally:
+        os.environ.pop('NICEGUI_USER_SIMULATION', None)
+        ui.navigate = Navigate()
+        ui.notify = notify
+        ui.download = download
 
 
 @pytest.fixture
 async def create_user(user: User) -> AsyncGenerator[Callable[[], User], None]:  # pylint: disable=unused-argument
     """Create a fixture for building new users."""
     prepare_simulation()
-    async with core.app.router.lifespan_context(core.app):
-        yield lambda: User(httpx.AsyncClient(transport=httpx.ASGITransport(core.app), base_url='http://test'))
-    ui.navigate = Navigate()
-    ui.notify = notify
-    ui.download = download
+    try:
+        async with core.app.router.lifespan_context(core.app):
+            yield lambda: User(httpx.AsyncClient(transport=httpx.ASGITransport(core.app), base_url='http://test'))
+    finally:
+        ui.navigate = Navigate()
+        ui.notify = notify
+        ui.download = download

tests/test_main_file_marker.py

@@ -3,14 +3,12 @@
 from nicegui.testing import Screen, User
 
 
-@pytest.mark.skip('This test breaks all following tests')
 @pytest.mark.xfail(raises=FileNotFoundError, strict=True)
 @pytest.mark.nicegui_main_file('non_existent_file.py')
 async def test_marker_injects_main_file_for_user_plugin(user: User):
     await user.open('/')
 
 
-@pytest.mark.skip('This test breaks all following tests')
 @pytest.mark.xfail(raises=FileNotFoundError, strict=True)
 @pytest.mark.nicegui_main_file('non_existent_file.py')
 def test_marker_injects_main_file_for_screen_plugin(screen: Screen):