Nullinjectorerror: no provider for FormBuilder (I’m importing ReactiveFormsModule)

Open app.component.spec.ts and add ReactiveFormsModule to imports array.

app.component.spec.ts

describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        ReactiveFormsModule <================================= add this
      ],
      declarations: [
        AppComponent,
        HoursCalculatorComponent
      ],
    }).compileComponents();
  }));