async-chai-sinon.js

"use strict";
var chai = require("chai");
var sinon = require("sinon");
var sinonChai = require("sinon-chai");
chai.should();
chai.use(sinonChai);

function asyncHello(name, delay, cb) {
  setTimeout(function() {
    console.log("running after ", delay);
    cb("hello " + name);
  }, delay);
}

suite('Mega Suite', function(){

  suite("testing async hello", function() {
    test('should call the callback', function(done) {
      var cb = sinon.spy();
      asyncHello("foo", 500, cb);

      cb.should.have.been.called();
      done();
    });
  });
});

package.json

$ cat package.json
{
  "name": "mocha-meetup",
  "version": "0.0.0",
  "description": "",
  "main": "index.js",
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "chai": "^1.9.1",
    "mocha": "^1.21.4",
    "sinon": "^1.10.3",
    "sinon-chai": "^2.5.0"
  },
  "scripts": {
    "test": "node_modules/.bin/mocha --ui=tdd test/*.js"
  }
}

Ken Powers has a great writeup on some of Sinon's advance features. I guess one approach is to use fake timers and skip using Mocha's done() functionality.

Based on that blog, I tweaked the test to look like:

suite('Mega Suite', function(){

  suite("testing async hello", function() {
    beforeEach(function () {
      // Overwrite the global timer functions (setTimeout, setInterval) with Sinon fakes
      this.clock = sinon.useFakeTimers();
    });

    afterEach(function () {
      // Restore the global timer functions to their native implementations
      this.clock.restore();
    });

    test('should call the callback', function() {
      var spy = sinon.spy();

      function asyncHello(name, delay, cb) {
        setTimeout(function() {
          console.log("running after ", delay);
          cb("hello " + name);
        }, delay);
      }

      asyncHello("foo", 1000, spy);
      this.clock.tick(999);
      spy.should.have.not.been.called;

      this.clock.tick(1);
      // Now the spy should have been called
      spy.should.have.been.called;

      spy.should.have.been.calledOnce;
    });
  });
});

Which works. Using done seems cleaner/simpler, though.