Tests for Promise.withResolvers

[peetklecha]

I was asked to open this issue to track test completeness for the Stage 3 Promise.withResolvers method. I'm pretty new to this so any suggestions for things that should go in this tracker would be very appreciated.

• boilerplate tests (e.g., length.js, name.js, prop-desc.js, not-a-constructor.js, builtin.js)
• throws a type error if receiver is not a constructor
• produces an object with the Object.prototype prototype
• produces an object with the keys resolve, reject, and promise
• the value of the promise property on the produced object is an instance of the receiver
• the values of the resolve and reject properties are both 1-place functions
• Receiver constructor does not have to extend built-in Promise
• Function body of the receiver constructor
  • throws
  • TypeError if it passes only zero or one parameter to the executor (because we can't get a resolve or reject)
  • nothing happens if it passes more than 2 parameters to the executor
  • TypeError if it passes a non-callable resolve to the executor
  • TypeError if it passes a non-callable reject to the executor
  • TypeError if it calls the executor twice
  • value of promise property if it returns a value that isn't an instance of itself

[ptomato]

Thanks! Added some suggestions from examining the existing tests for Promise.all.

[evilpie]

Assuming the built-ins/Promise/withResolvers directory contains all tests, what I am missing is test(s) that call the resolve/reject functions and make sure the promise object is correctly rejected/resolved.

[peetklecha]

thanks for the additions @ptomato ! i'm not sure i understand the first or last items in the sub-list you added there.

also do you know of an example of an existing Promise method that has a test for Reciever constructor does not have to extend built-in Promise?

[ptomato]

Sure, for the first item in the sub-list ("throws"): I meant we should test the case where the function body of the receiver's constructor throws an exception. Like this:

function MyPromise() {
  throw new Error("you can't call me");
}
Promise.withResolvers.call(MyPromise);

For the last item in the sub-list ("value of promise property if it returns a value that isn't an instance of itself") - since a constructor can override the object that it would normally return, and return an entirely different object that isn't an instance of that constructor, or isn't even a Promise. Like this:

class MyPromise extends Promise {
  constructor(...args) {
    super(...args);
    return { then: Promise.prototype.then };
  }
}
Promise.withResolvers.call(MyPromise);

For an existing example of "Reciever constructor does not have to extend built-in Promise" I don't know of one. But I did find https://github.com/tc39/test262/blob/main/test/built-ins/Promise/all/S25.4.4.1_A4.1_T1.js which is a test for the opposite, that Promise.all() fails when the receiver doesn't extend built-in Promise. So maybe I'm missing something in my reading of the spec for Promise.withResolvers(), and this should actually not work.