Fake timers are synchronous implementations of setTimeout and friends that Sinon.JS can overwrite the global functions with to allow you to more easily test code using them.

Fake timers provide a clock object to pass time, which can also be used to control Date objects created through either new Date(); or Date.now(); (if supported by the browser).

For standalone usage of fake timers it is recommended to use lolex package instead. It provides the same set of features (Sinon uses it under the hood) and was previously extracted from Sinon.JS.

{
    setUp: function () {
        this.clock = sinon.useFakeTimers();
    },

    tearDown: function () {
        this.clock.restore();
    },

    "test should animate element over 500ms" : function(){
        var el = jQuery("<div></div>");
        el.appendTo(document.body);

        el.animate({ height: "200px", width: "200px" });
        this.clock.tick(510);

        assertEquals("200px", el.css("height"));
        assertEquals("200px", el.css("width"));
    }
}

Fake timers API

var clock = sinon.useFakeTimers();

Causes Sinon to replace the global setTimeout, clearTimeout, setInterval, clearInterval, setImmediate, clearImmediate, process.hrtime, performance.now(when available) and Date with a custom implementation which is bound to the returned clock object.

Starts the clock at the UNIX epoch (timestamp of 0).

var clock = sinon.useFakeTimers(now);

As above, but rather than starting the clock with a timestamp of 0, start at the provided timestamp now.

Since sinon@2.0.0

You can also pass in a Date object, and its getTime() will be used for the starting timestamp.

var clock = sinon.useFakeTimers(config);

As above, but allows further configuration options, some of which are:

  • config.now - Number/Date - installs lolex with the specified unix epoch (default: 0)
  • config.toFake - String[ ] - an array with explicit function names to fake. By default lolex will automatically fake all methods except process.nextTick. You could, however, still fake nextTick by providing it explicitly
  • config.shouldAdvanceTime - Boolean - tells lolex to increment mocked time automatically based on the real system time shift (default: false). When used in conjunction with config.toFake, it will only work if 'setInterval' is included in config.toFake.

Please refer to the lolex.install documentation for the full set of features available and more elaborate explanations.

Since sinon@3.0.0

var clock = sinon.useFakeTimers([now, ]prop1, prop2, ...) is no longer supported. To define which methods to fake, please use config.toFake.

Important note: when faking nextTick, normal calls to process.nextTick() would not execute automatically as they would during normal event-loop phases. You would have to call either clock.next(), clock.tick(), clock.runAll() or clock.runToLast() (see example below). Please refer to the lolex documentation for more information.

Examples

Installs fake timers at January 1st 2017 and fakes setTimeout and process.nextTick only:

var clock = sinon.useFakeTimers({
                now: 1483228800000,
                toFake: ["setTimeout", "nextTick"]
            });

var called = false;

process.nextTick(function () {
    called = true;
});

clock.runAll(); //forces nextTick calls to flush synchronously
assert(called); //true

Install at the same date, advancing the fake time automatically (default is every 20ms), causing timers to be fired automatically without the need to tick() the clock:

var clock = sinon.useFakeTimers({
                now: 1483228800000,
                shouldAdvanceTime: true
            });

setImmediate(function () {
    console.log('tick'); //will print after 20ms
});

setTimeout(function () {
    console.log('tock'); //will print after 20ms
}, 15);

setTimeout(function () {
    console.log('tack'); //will print after 40ms
}, 35);

Using fake timers with async / await:

async function asyncFn() {

    await wait(100);

    console.log('resolved 1', Date.now());

    await wait(10);

    console.log('resolved 2', Date.now());
}

async function test() {

    const clock = sinon.useFakeTimers();

    setTimeout(() => console.log('timeout', Date.now()), 200);

    asyncFn(); // NOTE: no `await` here - it would hang, as the clock is stopped

    await clock.tickAsync(200);
}

// test() prints:
// - resolved 1 100
// - resolved 2 110
// - timeout 200

Note that in the above example, the synchronous clock.tick(200) would only print timeout 200 and resolved 1 200.

clock.tick(time); / await clock.tickAsync(time)

Tick the clock ahead time milliseconds.

Causes all timers scheduled within the affected time range to be called. time may be the number of milliseconds to advance the clock by or a human-readable string. Valid string formats are “08” for eight seconds, “01:00” for one minute and “02:34:10” for two hours, 34 minutes and ten seconds.

The tickAsync() will also break the event loop, allowing any scheduled promise callbacks to execute before running the timers.

clock.next(); / await clock.nextAsync()

Advances the clock to the the moment of the first scheduled timer, firing it.

The nextAsync() will also break the event loop, allowing any scheduled promise callbacks to execute before running the timers.

clock.runAll(); / await clock.runAllAsync()

This runs all pending timers until there are none remaining. If new timers are added while it is executing they will be run as well.

This makes it easier to run asynchronous tests to completion without worrying about the number of timers they use, or the delays in those timers.

The runAllAsync() will also break the event loop, allowing any scheduled promise callbacks to execute before running the timers.

clock.restore();

Restore the faked methods.

Call in e.g. tearDown.