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Graph/async-mock-return-type-mismatch

AntiPattern

Async Mock Return-Type Mismatch

async-mock-return-type-mismatch

Async mocks/fakes returning coroutines or awaitables where the code expects immediate objects (context managers, CompletedProcess, tuples) cause async with/await plumbing to break. The fallout is tests failing or event-loop blocking when real code would behave differently.

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Updated5/30/2026

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30 linked nodes

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

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Tension: despite that being what the react-query docs suggested. Outcome: This solved the type errors too.

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

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Have you tried awaiting the API response? — If that doesn't work, try initializing the table with mock data. Tension: to see if that works. Outcome: awaiting the API response.

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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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If you convert all operations to perform asynchronously (using `aiosqlite`) , the issue will be mitigated. — When a route in FastAPI is listed as asynchronous (`async def`). Tension: that doesn't fully solve the inherent single writer problem of Sqlite. Outcome: Here's a fully operational update of the FastAPI server logic:.

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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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Removing `async` before the function definition solved it. — class LoggingAPIRoute(APIRoute):. Outcome: def get_route_handler(self) -> Callable:.

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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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You need to install helper packages, such as `anyio` or `pytest-asyncio`. — Async fixtures do not work out of the box. Tension: NB. Use pytest_asyncio.fixture NOT pytest.fixture. Outcome: Example.

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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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I'd like to use `AsyncSession.sync_session` — async def get_session() -> AsyncSession: session = SessionLocal(). Tension: the code below fails with error. Outcome: use `AsyncSession.sync_session` but the code below fails with error.

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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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any time you have an I/O bound process with lots of idle time — waiting for user input, waiting for a TLS handshake. Tension: wrapping it in an async task can let other code run.

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

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Async-iterate the Result instead of awaiting `.records` — The driver's Result is async-iterable. Tension: Combined with a streaming HTTP response, records flow end-to-end without any single buffer. Outcome: records flow end-to-end without any single buffer.

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You forget to return the `fetch()` promise in the `requestRobots` thunk. Tension: it is giving only REQUEST_ROBOTS_PENDING and for other action when i run npm test it is giving undefined. Outcome: return fetch('https://jsonplaceholder.typicode.com/users').

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

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

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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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