Our integration tests are very similar to our unit tests, with the major difference being that our integration tests actually launch our application. Due to this, these tests run considerably slower than our unit tests:

WebStorm's detailed Mocha test logging shows that our integration tests suite runs about 12 times slower than our unit test suite. At this point, this time difference is clearly negligible, but as we scale up, it can easily became a bottleneck if our integration tests are taking too long. It's important to consider this hidden time cost of higher-level testing, and reinforce why it's a good idea to have more unit tests than integration tests in your application's testing strategy.

The chai-http library we used for writing these integration tests provides two key enhancements that make working with Express REST APIs much easier. The first is the micro HTTP request library built into chai-http, which is actually its own project called Super-Agent. Super-Agent is an ultra lightweight Node.js-based request library that we are using when we are configuring our request:

chai.request(API.connection).get('/api').end();

The Super-Agent API provides many useful ways to configure your integration test for a particular endpoint of your REST API:

.sortQuery(function(a, b) {
  return a.length - b.length; 
})

let cert = fs.readFileSync('cert.pem');

.cert(cert)

.timeout({
  response: 3000,
  deadline: 40000
})

import * as nocache from 'superagent-no-cache';
.use(nocache)

The Super-Agent official documentation also covers many additional details for advanced configuration options you might find useful for writing your integration tests, and is available at http://visionmedia.github.io/superagent/.

The other useful part of chai-http is the additional plugin assertions it adds to the Chai core assertion library. These assertions are oriented around the types of details you are most likely to want to assert with a response from a REST API:

There are many other plugins for Chai, similar to chai-http, that can further extend the power of your testings assertions within Chai.

One final detail worth noting is that we are launching our Express application without any database functionality. This is partially because this particular integration doesn't require it, but more than that, it's so that we can control that aspect of our tests directly instead of requiring our application to be aware that we are in a testing mode. You can very easily include the database configuration as well as the application, and set any mocks needed in the same hook we used to set up our Express application earlier. Try experimenting by adding this database configuration file back to any other integration tests you might want to create.