timer-test.js

function Timer () {
  this.hrStart = process.hrTime();
} 

Timer.prototype.end = function () {
  this.duration = process.hrTime(this.hrStart);
};

Timer.prototype.durationInMillis = function () {
  return this.duration[0] * 1000 + this.duration[1] / 1000 / 1000;
}

var timer = new Timer();
setTimeout(function () { timer.end(); assert.ok(timer.durationInMillis() >= 5); }, 5);