todo.service.spec.ts

it('createTodo should send a POST request and return the newly created item', (done) => {

    const item: Todo = {
      id: 2,
      userId: 2,
      title: 'Walk dog',
      completed: false
    };

    service.createTodo(item).subscribe(
      (data: Todo) => {
          expect(data).toBeDefined();
          expect(data).toEqual(item);
          done()
      },
      (error) => {
          fail(error.message)
      } 
    );

    const testRequest = httpMock.expectOne('https://jsonplaceholder.typicode.com/todos');
    expect(testRequest.request.method).toBe('POST');
    testRequest.flush(item);

  });