export class FormComponent {
  @Input() office: Office;
  @Input() officeLoading: boolean;

  ...
}

<form *ngIf="!officeLoading" (ngSubmit)="saveForm(form)" #form="ngForm" novalidate>
  <mat-form-field>
    <input
      class="company-name"
      matInput
      placeholder="Company Name"
      type="text"
      name="companyName"
      required
      #companyName="ngModel"
      [ngModel]="office?.companyName">
    <mat-error *ngIf="companyName.errors?.required && companyName.dirty">
      Company name is required
    </mat-error>
  </mat-form-field>
 ...
</form>

describe('FormComponent', () => {
  let component: FormComponent;
  let fixture: ComponentFixture<FormComponent>;
  let el: DebugElement;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        BrowserAnimationsModule,
        FormsModule,
        MatInputModule,
        OverlayModule,
        StoreModule.forRoot({}),
      ],
      declarations: [FormComponent],
      providers: [Actions, MatSnackBar, Store],
    }).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(FormComponent);
    component = fixture.componentInstance;
    el = fixture.debugElement;
    component.office = null;
    component.officeLoading = false;
    fixture.detectChanges();
  });

  it('should fill out form based on what comes back from API', () => {
    expect(component.office).toBe(null);
    expect(el.query(By.css('input.company-name')).nativeElement.value).toBe('');
    component.office = {
      companyName: 'Test Name',
    };
    component.officeLoading = false;
    fixture.detectChanges();

    expect(el.query(By.css('input.company-name')).nativeElement.value).toBe(
      'Test Name',
    );
  });
});