如何使用spyOn测试Promise.all的功能

Question

I'm a newbie to coding, so please ask if more information is necessary.

I want to test a then-block inside a Promise.all with spyOn, but the function get never called.

public foo(): void {
    const names = this.getNames();

    Promise.all(
      names.map(name =>
        this.nameService.doSomething( //some params )
      )
    )
      .then(result => this.controller.ok(names))
      .catch(error => {
        //do something
      });
  }

This is the test

it('should call controller.ok when name is set', () => {
    spyOn(nameService, 'doSomething').and.returnValue(Promise.resolve());
    spyOn(controller, 'ok');

    service.foo();

  expect(nameService.doSomething).toHaveBeenCalledWith({
      //some params
    });
  expect(controller.ok).toHaveBeenCalled(); //fails because never called
  });

I've debugged the code and the doSomething get called even with the right params, the code also reaches the then-block. But the test says, it never gets called, so somewhere in there the code breaks and I don't know why?

The catch-block is not called.

Answer 1

Promises representing the eventual completion or failure of an asynchronous operation. Within your test, when checking if controller.ok has been called, the Promise returned by Promise.all of method foo was not resolved yet. Therefore you need some sort of synchronization.

One possible solution could look as follows.

it('should call controller.ok when name is set', () => {
    const promises: Promise<any>[] = [];
    spyOn(nameService, 'doSomething').and.callFake(n => {
        const promise = Promise.resolve();
        promises.push(promise);
        return promise;
    });
    spyOn(controller, 'ok');

    service.foo();

    Promise.all(promises)
         .then(r => expect(controller.ok).toHaveBeenCalled());
});

The same can be achieved by using fakeAsync and tick from @angular/core/testing .

it('should call controller.ok when name is set', fakeAsync(() => {
    spyOn(nameService, 'doSomething').and.returnValue(Promise.resolve());
    spyOn(controller, 'ok');

    service.foo();
    tick();

    expect(controller.ok).toHaveBeenCalled();
}));