Node Tests with Mocha - 09 Dec 2014

Setting up testing for your node project can be a bit tricky due to a lack of conventions around testing. Here’s a simple example of setting up a test environment for an expressjs application with mocha.

The first thing we’ll want to do is install mocha and chai for our project. We can do that with the following commands.

npm install mocha --save-dev

npm install chai --save-dev

Mocha is our test runner, and we’ll be using chai to provide us with expectations. It essentially gives us access to:

  expect([1, 2]).to.have.length(2)

Once we’ve finished installing the required libraries, we can add a test script to our package.json file.

  "scripts": {
    "test": "find ./test -name '*_test.js' | xargs mocha -R spec"

Now when we run npm test, we’ll run every file in our test directory that ends in _test.js through mocha.

In addition to adding a test command, we can setup a mocha.opts file in our test directory to provide some sane defaults. Here’s an example file:

--require ./test/common.js
--reporter spec
--ui bdd
--timeout 60000
--slow 300

In this file, we’re telling it to load the common.js file in our test directory. We can then setup various globals and state in the common.js file that will be required in each of our tests. If you’re coming from a Ruby on Rails background, think of it like spec_helper.rb.

Here’s an example common.js file:

  global.chai = require('chai')
  global.expect = global.chai.expect = require('../index')
  process.env.NODE_ENV = process.env.NODE_ENV || 'test';
  process.env.TEST_ENV = process.env.TEST_ENV || 'test';

In this file, we’re setting up expect, chai, and app as global variables. This prevents us from having to require chai and chai.expect in all of our test files.

We’re also setting the NODE_ENV and TEST_ENV to test. This allows us to depend on the NODE_ENV when configuring our environment.

This basic setup can be expanded on to provide additional functionality, but helps to provide a starting point for most node applications.