Support testing the unhandled promise rejection

[kibertoad]

Clear and concise description of the problem

Currently vitest fails a test run if it detects an unhandled rejection having been thrown:

Vitest caught 1 unhandled error during the test run.
This might cause false positive tests. Resolve unhandled errors to make sure your tests are not affected.

However, sometimes this is a desireable behaviour, especially when we are testing global unhandled rejection handlers.

Suggested solution

Several options are possible:

• Only report as a problem unhandled rejections that were not handled during the test execution (e. g. if there is no `process.on('unhandledRejection' handler that would consume the event);
• Make it possible to mark tests as expecting the unhandled rejections (e. g. syntax similar to expect.assertions(1) - expect.unhandledRejections(1))

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[fregante]

I'm interested in this as well. With event handlers and callbacks in general, errors don't always make it back to the original call site, so they're thrown and uncaught/unhandled.

It'd be great if Vitest had an easy way "expect" these.

Last time I needed this I had to register my own unhandled rejection listener, probably breaking Vitest's own. Example:

https://stackoverflow.com/a/58844172/288906

[sheremet-va]

Last time I needed this I had to register my own unhandled rejection listener, probably breaking Vitest's own. Example:

I think this is what I would expect from the test to be honest.

I am not against having a built-in assertion for this. What API would you prefer? It would have to be async.

[kibertoad]

@sheremet-va It's perfectly fine to expect user to register their own unhandedRejection handler, key problem is that it doesn't seem possible at the moment, vitest reports the test as failed anyway