Jest test for Redux-Observable epic.

gamesEpic.test.js

import Rx from 'rxjs';
import { ActionsObservable } from 'redux-observable';
import { ajax } from 'rxjs/observable/dom/ajax';

import { loadGames } from '../../src/epics/games';

import { ajax } from 'rxjs/observable/dom/ajax';
jest.mock('rxjs/observable/dom/ajax', () => ({
  ajax: jest.fn(),
}));

const mockImplementation = () => {
  let callCount = 0;
  const responses = [
    null,
    [{
      gameId: 0,
    }], [{
      gameId: 0,
    }], [{
      gameId: 0,
    }], [{
      gameId: 0,
    }],
  ];
  return Rx.Observable.create((observer) => {
    if (callCount === 0) {
      observer.next(null);
    } else {
      observer.next({ response: responses[callCount] });
    }
    callCount += 1;
    observer.complete();
  });
};

test('loadGames polls games', () => {
  const inputValues = {
    a: { type: 'LOAD_GAMES', payload: { date: '2010-10-10' } },
    b: { type: 'LOAD_GAMES_CANCEL', payload: {} },
  };

  const expectedValues = {
    a: {
      type: 'SET_GAMES_LOADING',
      payload: { date: '2010-10-10' },
    },
    b: {
      type: 'RECEIVE_GAMES',
      payload: {
        date: '2010-10-10',
        items: [{
          gameId: 0,
        }],
      },
    },
  };

  const inputMarble = 'a-----b';
  const expectedMarble = '-abbbb------';

  const ts = new Rx.TestScheduler((actual, expected) => {
    expect(actual).toEqual(expected);
  });
  const action$ = new ActionsObservable(ts.createHotObservable(inputMarble, inputValues));
  const outputAction = loadGames(action$, null, ts, 10, 10);
  const ajaxMock = jest.fn();

  ajaxMock.mockReturnValue(mockImplementation());
  ajax.mockImplementation(ajaxMock);
  ts.expectObservable(outputAction).toBe(expectedMarble, expectedValues);
  ts.flush();
  expect(ajaxMock).toHaveBeenCalledTimes(1);
  expect(ajaxMock).toHaveBeenCalledWith({
    url: '../games/date/2010-10-10',
    responseType: 'json',
  });
});