Angular Mock field/property with Jasmine / Karma

Angular Mock field/property with Jasmine / Karma

In Jasmine/Karma testing for Angular, you can mock fields or properties by creating a spy or a mock object. Here's an example using both Jasmine spies and a custom mock object:

Suppose you have a service with a property someProperty that you want to mock:

// your.service.ts import { Injectable } from '@angular/core'; @Injectable({ providedIn: 'root', }) export class YourService { someProperty: string = 'OriginalValue'; // ... other methods or properties }

Now, let's say you want to mock someProperty in your Jasmine/Karma test:

Using Jasmine Spy:

import { TestBed } from '@angular/core/testing'; import { YourService } from './your.service'; describe('YourComponent', () => { let yourService: YourService; beforeEach(() => { TestBed.configureTestingModule({ providers: [YourService], }); yourService = TestBed.inject(YourService); }); it('should mock someProperty using Jasmine Spy', () => { // Create a spy on the property spyOnProperty(yourService, 'someProperty', 'get').and.returnValue('MockedValue'); // Access the property and expect the mocked value expect(yourService.someProperty).toBe('MockedValue'); }); });

Using a Custom Mock Object:

import { TestBed } from '@angular/core/testing'; import { YourService } from './your.service'; class MockYourService extends YourService { // Override the property with a mock value someProperty: string = 'MockedValue'; } describe('YourComponent', () => { let yourService: MockYourService; beforeEach(() => { TestBed.configureTestingModule({ providers: [{ provide: YourService, useClass: MockYourService }], }); yourService = TestBed.inject(YourService) as MockYourService; }); it('should mock someProperty using a custom mock object', () => { // Access the property and expect the mocked value expect(yourService.someProperty).toBe('MockedValue'); }); });

Choose the approach that best fits your testing scenario. Jasmine spies are more dynamic and can be used on existing objects, while a custom mock object gives you full control over the mock's behavior.

Examples

  1. "Angular mock service property with Jasmine"

    • Code:
      const mockService = jasmine.createSpyObj('YourService', ['propertyToMock']); mockService.propertyToMock.and.returnValue(mockedValue);
    • Description: Uses jasmine.createSpyObj to create a mock service and mocks a property using and.returnValue.

  2. "Angular mock component property with Jasmine"

    • Code:
      const fixture = TestBed.createComponent(YourComponent); const component = fixture.componentInstance; component.propertyToMock = mockedValue; fixture.detectChanges();
    • Description: Sets the value of a component property directly to mock it during testing.

  3. "Angular mock directive property with Jasmine"

    • Code:
      const fixture = TestBed.createComponent(YourComponent); const directiveInstance = fixture.debugElement.query(By.directive(YourDirective)).injector.get(YourDirective); directiveInstance.propertyToMock = mockedValue; fixture.detectChanges();
    • Description: Locates the directive instance within a component and sets its property to mock it.

  4. "Angular mock class property with Jasmine"

    • Code:
      spyOn(YourClass.prototype, 'propertyToMock').and.returnValue(mockedValue);
    • Description: Uses spyOn to mock a property of a class prototype.

  5. "Angular mock injected service property with Jasmine"

    • Code:
      TestBed.configureTestingModule({ providers: [ { provide: YourService, useValue: { propertyToMock: mockedValue } } ] });
    • Description: Configures the testing module to provide a mocked value for the injected service property.

  6. "Angular mock ViewChild property with Jasmine"

    • Code:
      const fixture = TestBed.createComponent(YourComponent); const component = fixture.componentInstance; component.yourViewChild.propertyToMock = mockedValue; fixture.detectChanges();
    • Description: Sets the value of a property on a ViewChild decorated element to mock it.

  7. "Angular mock input property with Jasmine"

    • Code:
      const fixture = TestBed.createComponent(YourComponent); const component = fixture.componentInstance; component.inputProperty = mockedValue; fixture.detectChanges();
    • Description: Sets the value of an input property directly to mock it during testing.

  8. "Angular mock output property with Jasmine"

    • Code:
      const fixture = TestBed.createComponent(YourComponent); const component = fixture.componentInstance; spyOn(component, 'outputProperty'); // Trigger an event that should invoke the output property fixture.detectChanges(); expect(component.outputProperty).toHaveBeenCalledWith(mockedValue);
    • Description: Uses spyOn to mock an output property and verifies that it is called with the expected value.

  9. "Angular mock ActivatedRoute property with Jasmine"

    • Code:
      TestBed.configureTestingModule({ providers: [ { provide: ActivatedRoute, useValue: { snapshot: { params: { propertyToMock: mockedValue } } } } ] });
    • Description: Configures the testing module to provide a mocked value for the ActivatedRoute property.

  10. "Angular mock form control property with Jasmine"

    • Code:
      const formGroup = new FormGroup({ 'propertyToMock': new FormControl(mockedValue) });
    • Description: Initializes a FormGroup with a FormControl containing the mocked value.

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