dependencyInjection.js

// Dependency Injection
const assert = require('assert')

function getAnimals(fetch, id) {
	return fetch('http://api.animalfarmgame.com/animals/' + id)
		.then(response => response.json())
		.then(data => data.results[0])
}

describe('getAnimals', () => {
	it('calls fetch with the correct url', () => {
		const fakeFetch = url => {
			assert( url === 'http://api.animalfarmgame.com/animals/123')
			return new Promise(function(resolve) {

			})
		}
		getAnimals(fakeFetch, 123)
	})

	it('parses the response of fetch correctly', (done) => {
		const fakeFetch = url => {
			return new Promise.resolve({
				json: () => Promise.resolve({
					results: [ { name: 'fluffykins' } ]
				})
			})
		}
		getAnimals(fakeFetch, 12345)
			.then(result =>  {
				assert(result.name == 'fluffykins')
				done()
			})
	})
})