Setting initial values to Angular form group for testing

Question

I'm writing a unit test for an Angular 7 reactive form that has its input values pre-filled with server data on ngInit. How can I set the values of this form so that it doesn't five me a "value undefined" error during testing?

This is my form being pre-filled on ngOnInit:

 ngOnInit() {
  this.userForm = this.formBuilder.group({
  id: [ this.user.id ],
  first_name: [this.user.first_name, Validators.required],
  last_name: [this.user.last_name, Validators.required],
});

This is the current (barebones) test code for the form:

//import modules

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

  beforeEach(async(() => {
    TestBed.configureTestingModule({
    imports: [
      MaterialModule,
      ReactiveFormsModule,
      FormsModule,
    ],
    declarations: [
      UserListItemComponent,
    ],
    schemas: [CUSTOM_ELEMENTS_SCHEMA]
  })
  .compileComponents();
  }));

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

it('should create', () => {
  component.userForm.setValue({
    id: 123,
    first_name: "john",
    last_name: "smith",
  });
  expect(component).toBeTruthy();
  });
});

However, the Karma test runner still says it's undefined for id. Is it because it's not pre-filling the data with setValue ?

Answer 1

Calling fixture.detectChanges(); will call ngOnInit() , but the user property is undefined. You can change your code like this:

fixture = TestBed.createComponent(UserListItemComponent);
component = fixture.componentInstance;
const user = {
//your properties here
};
component.user = user;
fixture.detectChanges();

Answer 2

You can have a function to update the form values, when testing:

function updateForm(id: string, first_name: string, last_name: string) {
        component.userForm.controls['id'].setValue(id);
        component.userForm.controls['first_name'].setValue(first_name);
        component.userForm.controls['last_name'].setValue(last_name);
    }

In the test case:

 it('should create form', () => {
  updateForm('1','john','smith');
  expect(component).toBeTruthy();
  expect(component.userForm.value).toBeTruthy();
});

Or you can pass the user object to component using:

`component.user = mockUser;`

And the form values will be set onInit.

Most likely the error you have because of undefined user property on component.