example of a Jest integration test

.babelrc

{
  "presets": ["es2015"]
}

api-wrapper.js

import axios from 'axios';

const baseUrl = 'http://example.com';

export function get(endpoint) {
  return axios.get(baseUrl + endpoint);
}

employees-fetcher.js

import { get } from './api-wrapper';

export async function fetchEmployees() {
  return await get('/employees');
}

package.json

{
  "name": "demo-jest-integration",
  "version": "0.0.1",
  "scripts": {
    "test": "jest"
  },
  "dependencies": {
    "axios": "0.17.1",
    "lodash.maxby": "4.6.0"
  },
  "devDependencies": {
    "babel-core": "6.26.0",
    "babel-jest": "21.2.0",
    "babel-preset-es2015": "6.24.1",
    "jest": "21.2.1"
  }
}

top-employee-provider.js

import maxBy from 'lodash.maxby';
import { fetchEmployees } from './employees-fetcher';

export async function calculateTopEmployee() {
  const allEmployees = await fetchEmployees();
  return maxBy(allEmployees, e => e.numOfSales)
}

top-employee-provider.test.js

import { calculateTopEmployee } from './top-employee-provider';
import { get } from './api-wrapper';

jest.mock('./api-wrapper');

test('returns the top-performing employee', async () => {
  mockApiResponse('/employees', [
    {name: 'foo', numOfSales: 1 },
    {name: 'bar', numOfSales: 2 }
  ]);

  const topEmployee = await calculateTopEmployee();

  expect(topEmployee).toEqual({ name: 'bar', numOfSales: 2 });
});

function mockApiResponse(endpoint, payload) {
  const successfulPromise = new Promise(resolve => process.nextTick(() => resolve(payload)));

  get.mockImplementationOnce(e => e === endpoint ? successfulPromise : Promise.reject());
}