testing that a component method calls another method

Question

Given this simple component :

import { Component} from '@angular/core';

@Component({
  selector: 'app-component'
})
export class AppComponent {
  foo() {
    this.bar();
  }

  bar() {
    console.log('hello');
  }
}

How come the following test won't validate that bar is called when I call foo

describe('AppComponent', () => {
  let component: AppComponent;

    beforeEach(() => {
    component = new AppComponent();
  }

  it('should foobar', () => {
    component.foo();
    spyOn(component, 'bar');
    expect(component.bar).toHaveBeenCalled();
  })

}

I get the failed test :

Expected spy bar to have been called.

Solution 1

You need to set up the spy before the method is called. Jasmine spys wrap function to determine when they are called and what they get called with. The method must be wrapped before the spied on method is called in order to capture the information. Try changing your test to match the following:

it('should foobar', () => {
    spyOn(component, 'bar');
    component.foo();
    expect(component.bar).toHaveBeenCalled();
})

Solution 2

it("should foobar", () => {
    const spy = spyOn(component, "bar");
    component.foo();
    expect(spy).toHaveBeenCalled();
  });