Jest Test Exercise - Unreachable internal variables

dispatch-close-now.js

import Dispatcher from './dispatcher'

// scoped to this file, not accessable outside
// used in the real world to prevent sending a
// window close tracking api request twice
let closeNowTriggered = false

const dispatchCloseNow = () => {
	if (!closeNowTriggered) {
		Dispatcher.trigger('window:closeNow')
		// prevent the trigger from being called twice
		// because the window is closing, it never
		// needs to be set back to false.
		closeNowTriggered = true
	}
}

export default dispatchCloseNow

dispatch-close-now.test.js

import Dispatcher from './dispatcher'
import dispatchCloseNow from './dispatch-close-now')

jest.mock('./dispatcher', () => ({
	trigger: jest.fn()
}))

describe('Close Window Dispatcher', () => {
	test('dispatchCloseNow triggers window:closeNow', () => {
		// execute
		dispatchCloseNow()

		// verify
		expect(Dispatcher.trigger).toHaveBeenCalledWith('window:closeNow')
		expect(Dispatcher.trigger).toHaveBeenCalledTimes(1)
	})

	test('dispatchCloseNow only calls window:closeNow once', () => {
		// execute
		dispatchCloseNow()
		dispatchCloseNow()

		// verify
		expect(Dispatcher.trigger).toHaveBeenCalledWith('window:closeNow')
		expect(Dispatcher.trigger).toHaveBeenCalledTimes(1)
	})
})

dispatcher.js

const Dispatcher = {
	trigger: eventName => {
		// simplified for sake of this example
		console.log(`${eventName} triggered!`)
	}
}

export default Dispatcher