This makes the promise returned by wait-for-expect resolve to the same value returned by the supplied callback

This would allow you to do something like this without having to repeat the call to getNumber:

const value = await waitForExpect(async() => {
    const val = await getNumber() // returns some number that might/should be greater than 50
    expect(val).toBeGreaterThan(50)
    return val
})
console.log(value > 50) // true
// Do something with value

My motivation for this is for use in the pptr-testing-library where it's wait function is (more or less) an alias for waitForExpect. In short I often want to wait for an element to exist on the page and then do something with the element. ie what I would like to do is this

const $button = await wait(() => $document.getByRole("button"))
// Do something with $button ...