Unit testing with Mocha and Momentjs

Question

I have a function that I'm trying to unit test with Mocha that uses moment .

function makeRange(timeagoMinutes) {
  var endDate = moment().toISOString();
  var startDate = moment().subtract(timeagoMinutes, 'm').toISOString();
  return startDate + ',' + endDate;
}

Here is what I have so far, but I'm having trouble figuring out what to do with moment . If I call makeRange(40) and run the tests, the string is different each time.

How can I fake the current time (ie moment().toISOString() ?

var rewire = require('rewire');
var controller = rewire('../thecontroller.js');
var moment = require('moment');

describe.only('makeRange', function() {
  var makeRange;

  beforeEach(function() {
    makeRange = controller.__get__('makeRange');
  });

  it('should return a string with a start date and end date', function() {
    //
  });
});

Answer 1

You are using rewire , so you can mock the moment module that's required in the controller to ensure that a known date/time is used:

describe.only('makeRange', function () {

  var makeRange;

  beforeEach(function () {

    var momentMock = function () {
      return moment('2016-08-31T09:00:00Z');
    };
    controller.__set__("moment", momentMock);
    makeRange = controller.__get__("makeRange");
  });

  it('should return a string with a start date and end date', function () {

    expect(makeRange(40)).to.equal('2016-08-31T08:20:00.000Z,2016-08-31T09:00:00.000Z');
  });
});