Add support for Promise about chai HOT 16 OPEN

that is what i'm leaning towards

think it makes sense to have native support for things like toThrow on a promise, etc

from chai.

An innate problem with adding promises to core is that all existing assertions synchronously throw, and there is no very clear signal as to what would then turn that into an asynchronous throw. chai-as-promised adds the eventually chainable property, which we could add but the await keyword is something that developers are much more likely to be aware of.

One way we could go about this change is to make all assertions return a Promise, but that's a big breaking change (though arguably one that gives us future flexibility for all kinds of async stuff). Another solution could be to extensively document how one would unpack promises within the existing assertions (which typically looks like expect(await ...), but the far bigger problem today exists with how to properly handle rejections which involves some code gymnastics.

from chai.

FWIW, my typical use-case for chai-as-promised (using mocha) is:

return expect(testClass.testFunction(args)).to.eventually.be.rejectedWith(Error);

from chai.

i recall in some other test libraries, some smarts were done to change the return type

e.g.

expect(someSyncThing).to.equal(10);

await expect(someAsyncThing).to.equal(10);

and basically have a conditional return:

function equal(expectation: unknown): T extends PromiseLike<unknown> ? Promise<void> : void;

but that may make my fancy types im doing in the typescript branch a bit more difficult 😬

since i'm not sure we can do a type guard return of a promise

from chai.