How to test a Angular pipe with own dependencies (injected with NG 15 inject())?

Question

A minimum working example, in a fresh Angular 15 CLI app:

• A (blank) service HelperService
• This service gets injected into DemoPipe with the new inject() call:

export class DemoPipe implements PipeTransform {
  private readonly helper = inject(HelperService);
  ...
}

The default pipe test created by NG-cli will fail, as the constructor call happens outside the DI context:

it('create an instance', () => {
  const pipe = new DemoPipe();
  expect(pipe).toBeTruthy();
});

Error: NG0203: inject() must be called from an injection context such as a constructor, a factory function, a field initializer, or a function used with `EnvironmentInjector#runInContext`. Find more at https://angular.io/errors/NG0203
        error properties: Object({ code: -203 })

Is there any wrapper I could use in Karma to provide the missing environment?

Answer 1

You can try the following:

describe('DemoPipe', () => {
 let pipe:DemoPipe;

  beforeEach(async () => {
    TestBed.configureTestingModule({ providers: [DemoPipe,HelperService] });
  });

it('create an instance', () => {
  pipe = TestBed.inject(DemoPipe);
  expect(pipe).toBeTruthy();
});

I tried and it works