bug(testing) ngOnChanges not called for component initialized via TestComponentBuilder

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[x] bug report
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

When creating a component via TestComponentBuilder the ngOnChanges-Callback is not executed. Having a component like this:

export class TimePickerComponent {

  @Input("time") private timeString = "";

  ngOnInit() {
    console.log("init")
  }
  ngOnChanges(changes) {
    console.log("changes");

    //do some transformation on the timeString- inputbinding
    }
  }
...
}

And creating the component in the test like this:

 it('display passed time in input fields', (done) => {
    tcb
      .createAsync(TimePickerComponent)
      .then(fixture => {
        let timePicker: TimePickerComponent = fixture.componentInstance;
        (<any>timePicker).timeString = "11:20:23";
     //   timePicker.ngOnChanges(null);  ->> needs to be called manually
        fixture.detectChanges();

        let hourInput = fixture.debugElement.query(By.css('#hours > input'));
        expect(hourInput.nativeElement.value).toBe("11");
        done();
      });
  });

the ngOnChanges callback of the component gets never called. (ngOnInit gets called by the way). To fix the test it is currently needed to call ngOnChanges manually…

Expected/desired behavior

ngOnChanges should be called while initializing the component

What is the motivation / use case for changing the behavior?

Being able to test components that use ngOnChanges callback without having to call the method manually

Please tell us about your environment:

• Angular version: 2.0.0-rc.4
• Browser: [all ]
• Language: [all]

[seanharr11]

It burdensome and arguably impractical to create a dummy parent component just to have it pass a value via Input() to trigger ngOnChanges(). This especially true when unit testing.

Why is it that detectChanges() cannot trigger the ngOnChanges() hook?

[mmmichl]

I would actually expect that fixture.detectChanges(); will trigger the ngOnChange callback as it anyways synchronises the state between the component and the view…

In any case, this needs to be clarified in the docs as suggested by @StdVectorBool.