Angular2 unit testing : testing a component's constructor

Question

All is in the title : how can one test what is done in the component\'s constructor ?

For your information, I am using a service that requires a setting

Answer 1

The simple way to test anything inside constructor function is to create component instance and then test it.

it('should call initializer function in constructor', () => {
  TestBed.createComponent(HomeComponent); // this is the trigger of constructor method
 expect(sideNavService.initialize).toHaveBeenCalled(); // sample jasmine spy based test case
});

One thing to note that, if you want to distinguish between constructor and ngOnInit, then don't call fixture.detectChanges() inside beforeEach(). instead call manually whenever you need.