Angular unit test case for this.document.body.setAttribute()

Question

document.body.setAttribute('data', 'data1') inside ngOnInint() in my component.

How can I write the unit test for this line?

Answer 1

You can create a unit test using Jasmine and TestBed in the following way:

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { YourComponent } from './your-component.component';

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

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [YourComponent],
    }).compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(YourComponent);
  });

  it('should set data attribute on document body in ngOnInit', () => {
    const spy = spyOn(document.body, 'setAttribute');
    fixture.detectChanges();
    expect(spy).toHaveBeenCalledWith('data', 'data1');
  });
});