I am facing an issue to write an unit test case in jasmine for my angular application. Have a reactive form and trying to reset a particular form control from a button click. Even though the scenario should be simple enough to test, it seems that I am missing something here.

Below is the code snippet from the app.

app.component.html:

<form [formGroup]="userForm" novalidate (ngSubmit)="onSubmit()">
  <div>
    <input
      type="text"
      id="fNameFld"
      name="fName"
      formControlName="fName"
      placeholder="First Name"
    />
    <button (click)="clearField('fName')" id="clrFName">
      Clear First Name
    </button>
  </div>

  <div>
    <input
      type="text"
      id="lNameFld"
      name="lName"
      formControlName="lName"
      placeholder="Last Name"
    />
    <button (click)="clearField('lName')" id="clrLName">Clear Last Name</button>
  </div>

  <div>
    <button type="submit">Submit</button>
  </div>
</form>

app.component.ts

import { FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
})
export class AppComponent implements OnInit {
  name = 'Angular ' + VERSION.major;
  userForm: FormGroup;

  constructor(private readonly fb: FormBuilder) {}

  ngOnInit() {
    this.userForm = this.fb.group({
      fName: this.fb.control(null),
      lName: this.fb.control(null),
    });
  }

  onSubmit() {
    console.log('Submitted Data', this.userForm.value);
  }

  clearField(controlName: string) {
    this.userForm.get(controlName).reset();
  }
}

Unit test code

it('should clear fName control when the "Clear First Name" button is clicked', () => { 
    const spy = spyOn(component, 'clearField');
    const clearBtn = fixture.debugElement.query(By.css("button#clrFName"));
    const form = component.userForm;
    
    form.patchValue({
      'fName': 'John,
      'lName': 'Doe'
    });
    
    clearBtn.nativeElement.click();
    fixture.detectChanges();
    expect(spy).toHaveBeenCalledTimes(1);  // passes
    expect(spy).toHaveBeenCalledWith('fName');  // passes
    expect(form.get('fName').value).toBeNull();  // fails: Expected 'John' to be null.
  });

Angular: 10.0.14

Angular CLI: 10.0.8

StackBlitz: https://angular-ivy-fc6rik.stackblitz.io