Use rest parameters to make expect.any() variadic

[zirkelc]

With expect.any() we can only have one type like expect.any(String). If we want to express an optional property that might be null or undefined, we have to use a 3rd party library.

If expect.any() were variadic, it could be called with multiple possible types expressing a logical-OR:

const user = isNew ? { name: "John" } : { id: 1, name: "Jane" };
expect(user).toEqual({ id: expect.any(Number, undefined) }); // ID can be undefined or Number

Making the signature variadic shouldn't break anything, but it would be a slight derivation from the Jest-style API.

[sheremet-va]

I am not convinced that we should allow additional arguments, but maybe we can add a new function like expect.oneOf(...args), so you example would looks like this:

expect(user).toEqual({
  id: expect.oneOf(expect.any(String), undefined))
})

[zirkelc]

Yes, that would be great! I wasn't sure you want to deviate from the Jest API, so I thought making expect.any() variadic is a minimally invasive solution.

[hi-ogawa]

It doesn't seem so from the doc https://jestjs.io/docs/expect#expectanyconstructor but does Jest support this? If so, then aligning with them should be fine.

Speaking of oneOf, chai seems to have something similar as non-asymmetric assertion https://www.chaijs.com/api/bdd/#method_oneof.

[zirkelc]

No, as far as I know Jest does not support expect.any(...args), but making this change wouldn't add another function (i.e. minimally invasive).

The alternative expect.oneOf(expect.any(String), undefined)) would be better IMO, but it would add a new function. If wasn't sure how strict you want to match the Jest APIs.

Let me know if you'd like me to try my hand at PR for this project.

[hi-ogawa]

Ah, got it 👍 You meant adding new expect.oneOf can be bigger deviation as it doesn't exists in Jest. For us, adding a new API is totally fine and encouraged when the new feature makes sense.

[zirkelc]

I created PR #6974 for this, let me know what you think! I used an array paramater for expect.oneOf([ ... ]) instead of variadic args, but I'm open to changing it.