Browser websockets can't be re-used within vitest test file.

[GeorgeLung]

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/GeorgeLung/msw-vitest-ws-example

Reproduction steps

npm test

Current behavior

For each file, of the two tests only the first passes. The second times out. This is because both of the promises (waiting on a websocket connection) don't resolve.

Expected behavior

All 4 tests to pass.

It's likely the pattern I'm attempting is the issue. In which case, I'd be grateful if the docs could be updated to demonstrate the correct pattern.

[kettanaito]

Hi, @GeorgeLung. Thanks for reporting this.

Can you please try removing worker.stop() from your Vitest fixture (here)? Let me know if that helps.

[GeorgeLung]

All 4 tests now pass. With the expected warning in the logs of:

 [MSW] Found a redundant "worker.start()" call. Note that starting the worker while mocking is already enabled will have no effect. Consider removing this "worker.start()" call.

I'm not familiar enough yet with the library to understand the implications of this. Is this just a case of updating the docs here: https://mswjs.io/docs/recipes/vitest-browser-mode/ and it's fine?

[kettanaito]

Yes, I don't believe you should be stopping the worker after the fixture (i.e. test) is done. The warning itself is something to think about. The intention here is to warn the developer about redundant worker.start() calls in their apps. In your case, I'd say it's okay calling .start() multiple times as they won't do anything.

We need to spend some time designing the proper experience around multiple worker.start() calls.