Add assert.rejects and assert.not.rejects methods for promises

[aral]

This implements the async equivalent of assert.throws() for promise rejections (and releated tests, based on the tests for throws).

While this can be handled via a workaround, having a separate method does cut down on boilerplate.

Instead of overloading throws, I feel it makes sense to have a separate method for promise rejections. This way throws is always sync and rejects is always async.

I understand if you’d rather just keep throws and the workaround, just wanted to share my addition upstream. Please feel free to close this pull request and its corresponding issue if you feel this is out of scope or complicates the API beyond what you’re comfortable with.

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Closes #131

[lukeed]

Suggested change

assert.unreachable('Function threw when it shouldn’t have');

[lukeed]

Suggested change

assert.unreachable('Function threw correct pattern when it should have thrown incorrect one');

[aral]

I added this in because I was confused when I changed the test to $.throws(() => { throw new Error('world') }, /world/); and it still passed. Wouldn’t the same thing happen if there was a regression in throws itself that would go unnoticed without this check?

[aral]

(I think this is – and the one above; same issue – are the only two I’m confused on. Accepted all other changes and happy to go with what you think is best for on these.)

[lukeed]

The assertion helper is saying: given X function, an error (a) should be thrown and (b) the thrown error should match {this condition}. The condition can be defined via a function, a RegExp, or a string.

So this test has X function, which happens to throw new Error('hello'), and the assertion is saying X must throw an Error that matches the /world/ pattern.

In the original test, this fails (obv because "hello" does not match /world) and so the assertions within the catch block run, and correctly find that the "Expected function to throw exception matching /world/ pattern" message appears, among others.

When you change the X to be:

$.throws(() => { throw new Error('world') }, /world/);

This doesnt fail the assertion, because "world" does match the /world pattern. The assertion passed. So in this case, the checks within the catch block never run.

Testing negated fail conditions can be a trip, haha

[jasikpark]

I kinda feel like it could be helpful to make that work via

$.throws(() => throw new Error('world') }).matches(new Error('world'));

which maybe that doesn't make sense.. but it'd be nice to be able to chain throws() with match() rather than having a regex over err.message 🤔

[lukeed]

Thanks but the current API is much preferred and has prior art from many existing test runners and/or assertion libraries. It would also add a bunch of additional changes for the same (but more verbose) result.

[dominikg]

is there anything i can help with to make this land? would love to use it in tsconfck tests.

[lukeed]

Not that I recall 👍 kept this open for the next feature release

[bleucitron]

Is there something similar to a .resolves() that would be an alias to .not.rejects() ?

[maraisr]

Friendly bump 😅