Angular mock Ionic component as input parameter

Question

I am using Angular 15 with Ionic 6. I am trying to test behavior of my custom component. As a testing framework I am using jest.

I have problem to test/mock @Input parameters which is the type of IonContent.

@Input() content: IonContent;

This is how my test setup look like, and I just do not know what to do with the IonContent input.

describe('MyCustomComponent', () => {
  let component: MyCustomComponent;
  let fixture: ComponentFixture<MyCustomComponent>;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [
        MyCustomComponent,
        IonicModule
      ]
    }).compileComponents();

    fixture = TestBed.createComponent(MyCustomComponent);
    component = fixture.componentInstance;
    component.content = // I do not know how to mock IonContent here ?
    fixture.detectChanges();
  })

score 1 · Answer 1 · edited Apr 30 '23 at 14:38

To mock the IonContent for testing, you can create a simple mock class that extends the IonContent class from Ionic. Since you're using Jest as your testing framework, you can leverage jest.fn() to create mock functions for the methods in IonContent that you want to test.

First, create a mock class for IonContent:

class MockIonContent extends IonContent {
  scrollToTop: jest.Mock;
  scrollToBottom: jest.Mock;

  constructor() {
    super(null, null); // You might need to pass in required dependencies, if any.
    this.scrollToTop = jest.fn();
    this.scrollToBottom = jest.fn();
  }
}

Now, update your test setup to use this mock class:

describe('MyCustomComponent', () => {
  let component: MyCustomComponent;
  let fixture: ComponentFixture<MyCustomComponent>;
  let mockIonContent: MockIonContent;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [
        MyCustomComponent,
        IonicModule
      ]
    }).compileComponents();

    fixture = TestBed.createComponent(MyCustomComponent);
    component = fixture.componentInstance;
    mockIonContent = new MockIonContent();
    component.content = mockIonContent; // Set the mock IonContent here
    fixture.detectChanges();
  });

  // Your tests go here
});

UPDATED ANSWER BASED ON COMMENTS BELOW:

// MockIonContent class with correct constructor values
class MockIonContent extends IonContent {
  scrollToTop: jest.Mock;
  scrollToBottom: jest.Mock;

  constructor(c: ChangeDetectorRef, r: ElementRef, z: NgZone) {
    super(c, r, z);
    this.scrollToTop = jest.fn();
    this.scrollToBottom = jest.fn();
  }
}

And the updated test setup:

describe('MyCustomComponent', () => {
  let component: MyCustomComponent;
  let fixture: ComponentFixture<MyCustomComponent>;
  let mockIonContent: MockIonContent;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [
        MyCustomComponent,
        IonicModule
      ]
    }).compileComponents();

    // Inject the required dependencies for MockIonContent constructor
    const changeDetectorRef = TestBed.inject(ChangeDetectorRef);
    const elementRef = TestBed.inject(ElementRef);
    const ngZone = TestBed.inject(NgZone);

    fixture = TestBed.createComponent(MyCustomComponent);
    component = fixture.componentInstance;
    mockIonContent = new MockIonContent(changeDetectorRef, elementRef, ngZone);
    component.content = mockIonContent; // Set the mock IonContent here
    fixture.detectChanges();
  });

  // Your tests go here
});

Thanks for the answer. I already tried it but this line was the biggest problem for me: super(null, null); Parameter I need to create IonContent cannot be null. This is the constructor: constructor(c: ChangeDetectorRef, r: ElementRef, z: NgZone); I do not know how to overcome this. — Milos, Apr 12 '23 at 13:14
I have updated my answer with information I found via Google..... — , Apr 12 '23 at 13:22
Thanks for the answer. Everything seems ok, I just cannot create instance of IonContent or MockIonContent. Seems that ChangeDetectorRef cannot be used in this way. I tried answer from this post: https://stackoverflow.com/questions/41421807/angular-2-how-to-mock-changedetectorref-while-unit-testing also without help. — Milos, Apr 12 '23 at 14:20

Angular mock Ionic component as input parameter

1 Answers1