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Graph/async-test-double-misuse

AntiPattern

Async Test Double Misuse

async-test-double-misuse

Async mocks and fakes are wrapped or executed incorrectly so the code under test receives coroutines instead of context managers or expected return objects, breaking async with/await semantics and causing loop blocking or closure errors.

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Updated6/25/2026

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30 linked nodes

MATCHESSolution

Instead of mocking local storage, I just need to access it directly — This is my test code using Jest + TypeScript. Tension: mocking local storage. Outcome: The final test should look like this:.

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Properly mock the Zustand store module by spying on/overriding the store export (the Zustand `create` result or the correct store factory export) to return a custom state and action implementation, then render the component and assert against the mocked behavior.

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Outcome: To solve this, I created a custom `MockPointerEvent` and mocked the necessary browser methods.

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Mock axios.get and await the assertion with waitFor()

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beforeEach(() => { vi.useRealTimers() }) — to the describe of the tests. Tension: I cannot modify and remove the setup scripts. Outcome: afterEach(() => { vi.useFakeTimers() }).

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delete the async from `fake_execute` — your `AsyncContextMock` needs to handle both use cases in your endpoint `await conn.execute()` and `async with conn.execute()`. Outcome: just make it a regular function so it returns your context manager directly, no coroutine wrapper.

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for `cursor.fetchone.return_value`, just use (2,) directly — `cursor.fetchone.return_value`. Tension: AsyncMock already makes it awaitable. Outcome: wrapping it again messes things up.

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The following test case is now passing. — mock-test.

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single worker running async loop. Outcome: So you have a single worker running async loop and you block that loop.

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Change the `mocked_app` and database `client` fixtures from `scope='session'` to `scope='function'` so each test gets a fresh app/client setup with a clean lifecycle.

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mock_client.update_one = AsyncMock(return_value=AsyncMock(matched_count=1, modified_count=1)). Outcome: Here the minimal code to make your example works.

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Use pytest_asyncio.fixture NOT pytest.fixture — @pytest_asyncio.fixture(scope='session', loop_scope='session'). Tension: async def my_fixture():. Outcome: yield 'foo'.

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Change the engine async fixture from session scope to function scope (remove scope="session") so all async fixtures/tests run on the same event loop, preventing the cross-loop Future/Task error.

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using `magicmock` to mock it could lead to unusual or unexpected behavior when checking for call counts — Since `get_item` might be an asynchronous function in your middleware. Tension: using `magicmock` to mock it could lead to unusual or unexpected behavior. Outcome: which is designed to work with async functions.

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Using `asyncio.sleep()` in a loop is perfectly fine. Tension: every time you `await` the sleep, you effectively yield control back to the event loop. Outcome: calling `asyncio.sleep(0)` does not sleep at all, but only yields control back to the event loop.

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use `pytest_asyncio` and the async fixture — If you don't want to utilize an `AsyncClient` like the one by `httpx`. Tension: ensuring that the FastAPI app's lifespan context correctly works.

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when I create the test client. Tension: The 'app' shortcut is now deprecated. Outcome: async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as async_test_client:.

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mock/fake/dummy S3 — simulate your desired test scenarios. Outcome: remove S3 from the problem and replace it with something that provides the same contract as S3.

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Mock `useAppDispatch` to return a `vi.fn()` dispatch function, then assert that the mock dispatch was called with the expected action (e.g., `resetStates()`).

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An async function was passed to useActionState.

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Or you can use `async/await` and `try/catch` — createAsyncThunk. Outcome: return data.

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Implement the mock as a properly typed React functional component (e.g., `const Modal: React.FC<ModalProps> = (...) => ...`) and ensure the mock returns a valid React element (e.g., `return <>{children}</>` or `return <View {...props}>{children}</View>`), with appropriate TypeScript/TSX configuration.

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Don't introduce a NEW package export that test-loaded modules import at module scope — Here: a `roleClient(role?)` helper in the consumer package (`etl/llm-route.ts`). Tension: it forces you to update every `vi.mock` factory, and missing one re-breaks CI.

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you want to mock away `m2`, but call the real `m1` method. Outcome: mockStatic(Myclass1.class, Mockito.CALLS_REAL_METHODS).

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@ExtendWith({ MockitoExtension.class, ApplicationExtension.class }) — To use TestFX to test a JavaFX application. Tension: how do you do both at the same time? Outcome: it works for this case.

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Alternately, you could treat tests with mocks as unit tests which don't involve JavaFX code.

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catch(TimeoutException | UnhandledAlertException e) — I was able to make the test pass with this code. Tension: I have to wait 160 seconds for the timeout to be thrown. Outcome: result = true;.

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I think it is better to use a custom context manager — if you need to isolate test methods from each other. Tension: you need to isolate test methods from each other. Outcome: here is what I am using.

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Rewrite the test as an async test and run it with an async test runner (e.g., pytest.mark.asyncio), using await on the async ORM methods (acreate/acount) instead of asyncio.run().

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Defer ALL database imports into the script's `main()` function. — Test file imports only the pure helpers — no DATABASE_URL needed, no mocks. Tension: dynamic `await import()` is slightly slower on first DB call. Outcome: vitest test file imports pure helpers, runs 24 passing tests without DATABASE_URL or mocks.

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