How to test forkJoin() operator with jasmine-marbles

Question

I created service which is sending data to back-end, data was filled by user in UI. User can also upload any file to send it to back-end too. I am trying to test this functionality with jasmine marbles.

Here is my service code:

export class FormSubmitService {
  constructor(private http: HttpClient) {}

  public submit(data, attachments) {
    const observables = [
      ...attachments.map((file) => this.uploadAttachment(file)),
    ];

    return forkJoin(...observables)
      .pipe(
        defaultIfEmpty([]),
        map((tokens) => {
          return tokens.map((tokenObj) => tokenObj.attachment_token);
        }),
        switchMap((tokens: string[]) => {
          const formData = {
            data,
            attachments: tokens,
          };

          return this.submitForm(formData);
        }),
      );
  }

  private uploadAttachment(attachment: File) {
    const attachmentData: FormData = new FormData();
    attachmentData.append('attachment', attachment, attachment.name);

    return this.http.post(
      '/some/form/endpoint/attachments',
      attachmentData,
    );
  }

  private submitForm(userData: UserData) {
    return this.http.post(
      `/some/form/endpoint/form`,
      userData,
    );
  }
}

If user adds one or more attachments, then before I send user data to back-end, I need to upload each attachment to back-end to get each attachment's token which later I am storing in array. I am doing it with forkJoin(), waiting till all attachments are uploaded and then using switchMap to submitting user data.

Here are two of my test cases (one working, one not working):

describe('SubmitFormData', () => {
  let service: FormSubmitService;
  let http: jasmine.SpyObj<HttpClient>;

  beforeEach(() => {
    http = jasmine.createSpyObj('HttpClient', ['post']);
    service = new FormSubmitService(http);
  });

  describe('#submit', () => {
    const file = new File([''], 'filename', { type: 'image/png' });
    const attachments = [file];
    const data = {
      name: 'name',
      description: 'description',
    };

    // NOT WORKING!
    it('submit with attachment', () => {
      const expected = cold('-a--b-', { a: ['token'], b: { id: 'id_123' } }); // FAIL!
      // const expected = cold('----'); // SUCCESS!
      http.post.and.returnValues(
        cold('-a-', { a: [{ attachment_token: 'token' }] }),
        cold('-a-', { a: { id: 'id_123' } }),
      );

      const output = service.submit(data, attachments);

      expect(output).toBeObservable(expected);
      expect(http.post).toHaveBeenCalled();
    });

    // WORKING!
    it('submit without attachment', () => {
      const response = {
        id: 'id_123',
      };
      const expected = cold('-a-', { a: response });
      http.post.and.returnValues(
        cold('-a-', { a: { id: 'id_123' } }),
      );

      const output = service.submit(data, []);

      expect(output).toBeObservable(expected);
      expect(http.post).toHaveBeenCalled();
    });
  });
});

Test where form data is without attachments is successful, but test where form data is with attachment fails.

Error message from failure:

✖ submit with attachment HeadlessChrome 71.0.3578 (Mac OS X 10.14.2) Error: Expected $.length = 0 to equal 2. Expected $[0] = undefined to equal Object({ frame: 10, notification: Notification({ kind: 'N', value: [ 'token' ], error: undefined, hasValue: true }) }). Expected $[1] = undefined to equal Object({ frame: 40, notification: Notification({ kind: 'N', value: Object({ id: 'id_123' }), error: undefined, hasValue: true }) }).

Seems like output is not emitting observable in failed test and is undefined, but question is - why? Because in another test it emitting it when not sending attachment and using forkJoin().

Anyone have idea why it could be like that? Thanks!

Answer 1

Fixed this issue, problem was with first observable which was returned from http.post call - cold('-a-', { a: [{ attachment_token: 'token' }] }),. It wasn't emitting new observable and in this point all test stopped. Changed it to of({ attachment_token: 'token' }), and test is successful.

Here is a code:

it('submit with attachment', () => {
  const response = {
    id: 'id_123',
  };
  http.post.and.returnValues(
    of({ attachment_token: 'token' }),
    cold('-a', { a: response }),
  );
  const expected = cold('-a', { a: response });

  const output = service.submit(data, attachments);

  expect(output).toBeObservable(expected);
  expect(http.post).toHaveBeenCalledTimes(2);
})