MSW sometimes still handles requests after worker is stopped

[diego-aquino]

Prerequisites

• I confirm my issue is not in the opened issues
• I confirm the Frequently Asked Questions didn't contain the answer to my issue

Environment check

• I'm using the latest msw version
• I'm using Node.js version 20 or higher

Browsers

Chromium (Chrome, Brave, etc.)

Reproduction repository

https://github.com/diego-aquino/msw-worker-stop-bypass-issue

Reproduction steps

1. pnpm install
2. pnpm test

Current behavior

Starting in msw@2.11.2, I found out that workers sometimes handle requests even after worker.stop() is called.

In the reproduction repository, this expect sometimes passes, sometimes fails.

https://github.com/diego-aquino/msw-worker-stop-bypass-issue/blob/main/example.browser.test.ts#L22-L27

  worker.stop();

  // This expect sometimes passes, sometimes fails.
  await expect(async () => {
    await fetch(`${baseURL}/users`);
  }).rejects.toThrowError(TypeError);

From my tests, I did not see this issue happening with server.close(), neither with worker.stop() and server.close() before 2.11.2 (I tested 2.11.1).

Expected behavior

I expected all requests made after worker.stop() was called to not be handled.

[kettanaito]

Released: v2.13.4 🎉

This has been released in v2.13.4.

• 📄 Release notes
• 📦 View on npm

Get these changes by running the following command:

npm i msw@latest

---

Predictable release automation by Release.

[diego-aquino]

Hi, @kettanaito. I'm not sure that this issue is fixed.

I upgraded the reproduction repository to msw@2.13.4 and the problem persists.

Also, the new tests in #2668 still fail non-deterministically even against main:

pnpm test:browser in-flight-request.test.ts

...

  3 failed
    [chromium] › test/browser/msw-api/setup-worker/stop/in-flight-request.test.ts:89:3 › bypasses requests immediately made after the worker was stopped, considering no default response (2) 
    [chromium] › test/browser/msw-api/setup-worker/stop/in-flight-request.test.ts:89:3 › bypasses requests immediately made after the worker was stopped, considering no default response (12) 
    [chromium] › test/browser/msw-api/setup-worker/stop/in-flight-request.test.ts:89:3 › bypasses requests immediately made after the worker was stopped, considering no default response (23) 
  99 passed (22.6s)

Let me know if you have any recommendations about how to approach this problem. I can help implement/validate/review the fix if you are interested. #2683 looks related.

[kettanaito]

@diego-aquino, yeah, you are right. The test is flaky. I've run it multiple times locally before the release, but I can verify that it fails 1/10 times for me. There has to be some race still happening somewhere. I really hope it's just an incorrectly orchestrated test.

You're saying it's still happening for you. Is that still reproducible on the repo you shared above?

[diego-aquino]

You're saying it's still happening for you. Is that still reproducible on the repo you shared above?

@kettanaito, unfortunately yes. I updated the repo yesterday and the tests still fail non-deterministically between 1/2 and 2/3 of the time.

The test itself is very simple:

for (let testNumber = 1; testNumber <= 100; testNumber++) {
  it(`bypasses requests made after the worker was stopped (test ${testNumber})`, async () => {
    await worker.start({ quiet: true });

    let response = await fetch(`${baseURL}/users`);
    expect(response.status).toBe(200);
    expect(await response.json()).toEqual([]);

    worker.stop();

    // This expect sometimes passes, sometimes fails.
    await expect(async () => {
      await fetch(`${baseURL}/users`);
    }).rejects.toThrowError(TypeError);
  });
}

AssertionError: promise resolved "undefined" instead of rejecting

- Expected: 
Error {
  "message": "rejected promise",
}

+ Received: 
undefined

 ❯ example.browser.test.ts:27:7
     25|     await expect(async () => {
     26|       await fetch(`${baseURL}/users`);
     27|     }).rejects.toThrowError(TypeError);
       |       ^
     28|   });
     29| }

 Test Files  1 failed (1)
      Tests  68 failed | 32 passed (100)
   Start at  17:20:40
   Duration  659ms