Adventures in Unit Testing 3

index.test.js

const someFunction = require('./index');
const rewire = require('rewire');

let app;
beforeEach(() => {
  someFunction();
  app = rewire('./index.js');
});

test('it should increment evtCount', () => {
  const evtCount = app.__get__('evtCount');
  const somePrivateFunc = app.__get__('somePrivateFunction');
  somePrivateFunc();
  expect(evtCount).toEqual(1);
});

test('it should call somePrivateFunction on the foo event', () => {
  const privateFuncMock = jest.fn();
  app.__set__('somePrivateFunction', privateFuncMock);
  const emitter = app.__get__('customEmitter');
  emitter.emit('foo', 'bar');
  expect(privateFuncMock).toHaveBeenCalled();
});