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Graph/async-boundary-mismatch

Pattern

Async Integration Mismatches

async-boundary-mismatch

Async boundaries fail when mocks, timeouts, and test fixtures return the wrong async shape (e.g., coroutines without aenter/aexit or timeouts that defer work) causing sync paths to fall back, rows to be marked pending, and telemetry to spike.

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Public graph metadata

Updated7/30/2026

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30 linked nodes

Zustand persist middleware does not write during the test setup

the tests timeout — when using MSW + Testing Library + Tanstack Query. Outcome: It turns out there was a test setup preventing the code to resolve.

Zone mismatch. — during runApp. Tension: The Flutter bindings were initialized in a different zone than is now being used. Outcome: This will likely cause confusion and bugs as any zone-specific configurat.

Sentry debug mode repeatedly prints logging output and captures errors, but the integration does not work as expected when testing with an intentional exception.

requests with the forbidden fields sailed through to the write path. Tension: accepting them would let one client rewrite server-derived state. Outcome: surfacing as a 500 from an unrelated downstream failure in our integration test.

the mock-test is giving me an error — I have `async with connection.execute(query) as cursor:` block in my endpoint. Tension: the non-mock test is passing, but the mock-test is giving me an error. Outcome: delete the async from `fake_execute` just make it a regular function so it returns your context manager directly.

the background job never runs — my `BackgroundTasks` only execute when declared inside an async dependency. Tension: No exception is raised, the route returns normally. Outcome: If I move the `bg.add_task()` call into the route itself, it works as expected.

facing error that `event loop is closed` — I have been working on yet another API using FastAPI and trying to write test cases for the APIs. Tension: using `asyncpg` driver/library to connect to the main db and for testcases using `aiosqlite` driver/library. Outcome: re-run the tests and report back on if it mitigates the issue.

some events are asynchronous and not come from a frontend request.

the two requests are executed "in parallel." — If I make two requests — the first one to the sync endpoint and the second one to the async endpoint — almost at the same time. Tension: I expected the event loop to be blocked. Outcome: the two requests are executed "in parallel.".

The object should be created within an async function or provide loop directly. Outcome: How to properly test my application? It looks like I have to mock kafka-functionality.

Mock call count stays zero for patched async method in pytest

print(session.sync_session.scalars(stmt)) # fails with — @app.post('/users') async def get_users(session: AsyncSession = Depends(get_session)). Tension: I'd like to use `AsyncSession.sync_session` but the code below fails with error. Outcome: the code is a simplified version of real case.

Outcome: integration tests fail with confusing downstream symptoms.

Unit tests cannot deterministically simulate S3 upload failure

An async function was passed to useActionState, but it was dispatched outside of an action context. — after submitting. Tension: Either pass the dispatch function to an `action` prop, or dispatch manually inside `startTransition`.

The middleware fetches an Azure token using async logic, but RTK-Query proceeds without waiting, so requests are sent before the token is available. As a result, the token is not present at the correct time for data fetching.

createAsyncThunk() does not wait for AuthService.login() to finish

createListenerMiddleware does not fire when the async thunk finishes and extraReducers run

one of my integration tests affects the other. Tension: Will affect this get list of customer test.

Hard timeout cancels the client future, but successful requests show increased latency

The return type of `asyncConnectAndHandshake` function should be a promise that can be either used in a coroutine with co_await or in a regular function with `operator()`. Tension: This line of code should be executed when promise1 is completed. Outcome: Should I use async_compose?

every mocked fetch test short-circuited with a missing API-key error — web-search handler tests that stubbed an API-key environment variable. Tension: ESM imports are evaluated before the test's stub took effect.

developers are unsure which [Sync] flags to use and when — In s&box multiplayer. Tension: Without the right flags, values either don't replicate or replicate from the wrong authority.

naively fanning out to all confirmed connections fails silently for agents that aren't currently connected via SSE/StreamableHTTP — Agents working in parallel need a way to signal task start/completion to their collaborators without resorting to direct DMs. Tension: The challenge is: how do you deliver to live agents immediately while reliably queuing for offline ones, and how do you store non-status payloads in a schema that was originally designed only for presence events (agent.online/offline)?

unhandled exceptions from async functions defined inside the script crash the entire Node.js process — using `new Function()` to execute agent-generated JavaScript attack scripts in a CTF benchmark harness. Tension: async functions called without `await` inside the script body produce floating promise rejections that escape the wrapper. Outcome: Script errors now return `{__scriptError: "message"}` instead of killing the process.

async fixtures decorated with @pytest.fixture are no longer auto-detected — Starting with pytest-asyncio 0.23.

Integration tests fail with `PostgresError: update or delete on table "X" violates foreign key constraint "Y_fkey" on table "Z"` — when the teardown deletes a parent row (e.g., a test agent/user). Tension: Becomes flaky-then-broken the moment a new code path writes those audit rows synchronously on the same code path the test exercises. Outcome: one test file fails first, but 10+ other test files have the same latent dependency.

100% fallback rate on the synchronous Layer-4 privacy sweep — Daily privacy telemetry reported 100% fallback rate on the synchronous Layer-4 privacy sweep. Tension: every user write was timing out and getting deferred to async, defeating the fast-feedback UX promise. Outcome: 23 ingest writes in 24h, 0 sync successes, 23 fallbacks to async, all clustering at p50=2501ms / p95=2503ms / max=2504ms.

Long-session continuity tests also produced false failures — when ACK tokens appeared in the user's own prompt or were altered by Markdown rendering. Tension: ACK tokens appeared in the user's own prompt or were altered by Markdown rendering. Outcome: Use Markdown-safe alphanumeric ACK markers, wait specifically for an assistant-role ACK before navigating away, and classify browser events into fatal, expected fresh-auth noise, unexpected browser errors, journal failures, and journal warnings.

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