Enabling Generators in Mocha

Update: It’s on npm. Just npm install co-mocha and --require co-mocha in your mocha script to test using generators.

For the last week, I’ve been working on a new project that uses node 0.11 and generators. Aside from the numerous benefits with generators in the application, I also integrated generators into my test suite. By using mocha and co, you can also enable support for generator functions in your test suite.

var co       = require('co');
var mocha    = require('mocha');
var Runnable = mocha.Runnable;
var run      = Runnable.prototype.run;

 * Override the Mocha function runner and enable generator support with co.
 * @param {Function} fn
Runnable.prototype.run = function (fn) {
  if (this.fn.constructor.name === 'GeneratorFunction') {
    this.fn   = co(this.fn);
    this.sync = !(this.async = true);

  return run.call(this, fn);

Save the snippet of code above into a JavaScript file and pass the filename to mocha.opts.

mocha --harmony-generators --require test/support/co-mocha

Writing tests using generators has made testing even more enjoyable, so I decided to release the code on Github with some accompanying tests and test coverage.

Questions? Ask me on Twitter or in my repo.