Feature: ability to add async matchers using expect.extend

[danrr]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
A custom matcher add using expect.extend needs to synchronously return an object containing pass and message fields.

What is the expected behavior?
Allow async functions to be used as matchers that return a promise which eventually resolves to an object containing pass and message. These would be subject to the usual timeout.

My use case would be to execute async operations on a custom snapshot inside the matcher in a way that's transparent to the user.

[cpojer]

This seems quite complex, I don't think we'll be adding this at this time. You can already use expect(…).resolves.to<Matcher>() to simplify working with async data. Matchers expect to be executed synchronously and async operations can be wrapped around them using Promises.

[danrr]

That's not quite the use case here.

expect would be passed stuff that's sync and the async stuff needs to happen after .resolves would have done anything.

[entropitor]

I also would want this if possible. The problem is that I want to abstract away some test logic into a custom jest matcher. However, unfortunately, some API's that I need to use return promises, so I cannot possibly make it a sync matcher

[dowsanjack]

This would actually be useful for me and my team as well. Does someone has any plans to implement this?

[SimenB]

If you can provide a PR which is not super complex, we might be able to merge it. No guarantees, though.

[github-actions]

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