index.test.js

import Emitter from '.'

describe('Emitter', () => {
  let sub
  const callback1 = jest.fn()
  const callback2 = jest.fn()
  const emitter = new Emitter()

  test('should trigger nothing', () => {
    emitter.emit('event', 'foo')
    expect(callback1).not.toHaveBeenCalled()
  })

  test('should trigger 1 callback', () => {
    sub = emitter.subscribe('event', callback1)
    emitter.emit('event', 'foo')
    expect(callback1).toHaveBeenCalledTimes(1)
    expect(callback1).toHaveBeenCalledWith('foo')
  })

  test('should trigger 2 callbacks', () => {
    emitter.subscribe('event', callback2)
    emitter.emit('event', 'bar', 'baz')
    expect(callback1).toHaveBeenCalledTimes(2)
    expect(callback1).toHaveBeenCalledWith('bar', 'baz')
    expect(callback2).toHaveBeenCalledTimes(1)
    expect(callback2).toHaveBeenCalledWith('bar', 'baz')
  })

  test('should release first callback, and call the second', () => {
    sub()
    emitter.emit('event', 'meow')
    expect(callback1).toHaveBeenCalledTimes(2) // same number as before
    expect(callback2).toHaveBeenCalledTimes(2)
    expect(callback2).toHaveBeenCalledWith('meow')
  })

  test('should return the return values of all the events in the callstack', () => {
    emitter.subscribe('myEvent', () => 1)
    emitter.subscribe('myEvent', () => 2)
    emitter.subscribe('myEvent', () => true)
    const result = emitter.emit('myEvent')
    expect(result).toEqual([1, 2, true])
  })
})