cannot read properties of undefined reading subscribe testing jasmine angular

Question

Hi I trying to test http request but , when I call a function in the ngOnInit it show me that message "cannot read properties of undefined" can somebody help me?

this is my test


  it('xxxx', () => {
    userServiceSpy.getUser.and.returnValue(of());
    const spygetUserTwo = spyOn(
      component,
      'getUserTwo'
    ).and.callThrough();
    component.ngOnInit();
    expect(spygetUserTwo).toHaveBeenCalled();
  });
```

The component

```
ngOnInit(): void {
    this.getUserTwo();
  }

  getUserTwo() {
    this.userService.getUser().subscribe(
      (val: any) => {
        console.log('xxx', val);
        this.user = val;
      },
      (err) => {
        console.log('err', err);
      }
    );
  }
```

AliF50 · Accepted Answer · 2022-08-10 12:53:45Z

0

I bet you the issue is that you're calling fixture.detectChanges() first before calling component.ngOnInit().

fixture = TestBed.createComponent(Component);
component = fixture.componentInstance;
fixture.detectChanges(); // Remove this line

The first fixture.detectChanges() you call is when ngOnInit is called and since you have not mocked this.userService.getUser() before this fixture.detectChanges(), you get that issue of cannot read property of undefined.

answered Aug 10, 2022 at 12:53

AliF50

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8 Comments

Ricardo Tovar Over a year ago

Hi,so, every time i call fixture.detectChanges(), the lifecycle is executed?

Ricardo Tovar Over a year ago

Isn't it best practice to place it beforeeach?

AliF50 Over a year ago

Hello, not every time. The first time. Every time after the first time, the HTML just gets updated with the new properties.

AliF50 Over a year ago

It could be best practice to place it beforeEach so make sure everything in the ngOnInit is mocked properly before this fixture.detectChanges() or else you will have issues like your question.

Ricardo Tovar Over a year ago

Hi,so, every time i call fixture.detectChanges(), the lifecycle is executed?

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