Question

I would like to mock the Date constructor so that whenever I call new Date(), it always return specific time.

I found Sinon.js provide useFakeTimers to mock time. But the following code doesn’t work for me.

sinon.useFakeTimers(new Date(2011,9,1));

//expect : 'Sat Oct 01 2011 00:00:00' ,

//result : 'Thu Oct 27 2011 10:59:44‘
var d = new Date();

Answer 1

sinon.useFakeTimers accepts a timestamp (integer) as parameter, not a Date object.

Try with

clock = sinon.useFakeTimers(new Date(2011,9,1).getTime());
new Date(); //=> return the fake Date 'Sat Oct 01 2011 00:00:00'

clock.restore();
new Date(); //=> will return the real time again (now)

If you use anything like setTimeout, make sure you read the docs because the useFakeTimers will disrupt the expected behavior of that code.