todo.service.spec.ts

fdescribe('updateTodos', () => {
    let displayErrorSpy: jasmine.Spy;

    beforeEach(() => {
      displayErrorSpy = spyOn(service, 'displayError');
    })

    it('should display an error message if the request is unauthorized', (done) => {
      service
        .updateTodo({ id: 1, userId: 1, title: 'Walk dog', completed: true })
        .subscribe(
          (data => {
            expect(data).toBeNull();
            expect(displayErrorSpy).toHaveBeenCalledWith('Unauthorized request');
            done();
          }),
          (error: HttpErrorResponse) => { fail('The Observable is not supposed to fail') }
        
      );

      const testRequest = httpMock.expectOne('https://jsonplaceholder.typicode.com/todos/1');
      expect(testRequest.request.method).toBe('PUT');
      testRequest.flush(null, { status: 401, statusText: 'Unauthorized request'});

    });
  });