What is the best way to test an Angular component that relies on a helper method which utilizes the TranslateService?

I have a unique custom Validator that utilizes ngx-translate

export class CustomValidator {
  static translation: TranslateService;

  static setTranslationService( translation: TranslateService): void {
    CustomValidator.translation = translation;
  }

  static required(messageKey: string = 'COMMON.VALIDATORS.REQUIRED') {
    const message = this.translation.instant(messageKey);
    return (control: AbstractControl): ValidationErrors | null => {
      return control.value ? null : { required: message };
    };
  }
}

I am configuring the translateService in my app.component, as follows:

export class AppComponent implements OnInit, AfterViewInit {
  constructor(private translateService: TranslateService) { }

  ngOnInit() {
    CustomValidator.setTranslationService(this.translateService);
  }
}

This setup works seamlessly. However, when I attempt to test a component utilizing the CustomValidator, an error is triggered:

TypeError: Cannot read properties of undefined (reading 'instant')

In order to address this issue, I experimented with creating a MockCustomValidator and including it as a provider

describe('MainLayoutComponent', () => {
  let component: MainLayoutComponent;
  let fixture: ComponentFixture<MainLayoutComponent>;
    
  beforeEach(async () => {
    await TestBed.configureTestingModule({
      imports: [
        TranslateTestingModule.withTranslations({
          en: require('../../../../../assets/i18n/en.json'),
        })
      ], providers: [
        { provide: CustomValidator, useClass: MockCustomValidator }
      ]
    }).compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(MainLayoutComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
}

Unfortunately, the error persists. Any suggestions on the best approach to resolve this?

Answer №1

After some troubleshooting, I was able to find a solution without mocking the custom validator directly. Instead, I mocked the TranslateService using an instant method and adjusted my test like this:

describe('MainLayoutComponent', () => {
    let component: MainLayoutComponent;
    let fixture: ComponentFixture<MainLayoutComponent>;
    
    beforeEach(async () => {
      await TestBed.configureTestingModule({
        imports: [
          TranslateTestingModule.withTranslations({
            en: require('../../../../../assets/i18n/en.json'),
          })
        ]
      }).compileComponents();
    });

    beforeEach(() => {
      CustomValidator.setTranslationService(new MockTranslateService());
      fixture = TestBed.createComponent(MainLayoutComponent);
      component = fixture.componentInstance;
      fixture.detectChanges();
    });

    it('should create', () => {
      expect(component).toBeTruthy();
    });
}

The only downside is that I had to change the type in the CustomValidator from TranslateService to any so that I could set the mock class instead.

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