raf-stub

Accurate and predictable testing of requestAnimationFrame and cancelAnimationFrame.

What can raf-stub enable you to do?

Step through requestionAnimationFrame calls one frame at a time
Continue to call requestionAnimationFrame until there are no frames left. This lets you fast forward to the end of animations.
Clear out all animation frames without calling them
Control animations that are orchestrated by third party libraries such as react-motion
Control time values passed to your requestAnimationFrame callbacks

This is not designed to be a polyfill and is only intended for test code.

Basic usage

// assuming node running environment so 'global' is the global object

import createStub from 'raf-stub';

const render = () => {
  return requestAnimationFrame(() => {
    console.log('animate allthethings!');
  });
};

describe('stub', () => {
  let stub;

  beforeEach(() => {
    stub = createStub();
    sinon.stub(global, 'requestAnimationFrame', stub.add);
    sinon.stub(console, 'log');
  });

  afterEach(() => {
    global.requestAnimationFrame.restore();
  });

  it('should allow us to execute requestAnimationFrame when we want', () => {
    render();

    stub.step();

    // console.log => animate allthethings!
    expect(console.log.called).to.be(true);
  });

  it('should allow us to cancel requestAnimationFrame when we want', () => {
    const id = render();

    stub.remove(id);
    stub.step();

    // *crickets*
    expect(console.log.called).to.be(false);
  });
});

Replace existing `requestAnimationFrame`

import { replaceRaf } from 'raf-stub';

// override requestAnimationFrame and cancelAnimationFrame with a stub
replaceRaf();

const render = () => {
  return requestAnimationFrame(() => {
    console.log('animate allthethings!');
  });
};

describe('stub', () => {
  it('should allow us to execute requestAnimationFrame when we want', () => {
    render();

    requestAnimationFrame.step();

    // console.log => animate allthethings!
    expect(console.log.called).to.be(true);
  });

  it('should allow us to cancel requestAnimationFrame when we want', () => {
    const id = render();

    cancelAnimationFrame(id);
    requestAnimationFrame.step();

    // *crickets*
    expect(console.log.called).to.be(false);
  });
});

Installation

## npm
npm install raf-stub --save-dev

## yarn
yarn add raf-stub --dev

stub

Created by createStub()

type signature

type Stub = {|
  add: (cb: Function) => number,
  remove: (id: number) => void,
  flush: (duration?: number) => void,
  reset: () => void,
  step: (steps?: number, duration?: number) => void,
|};

An isolated mock that contains it's own state. Each stub is independent and have it's own state.

Note changing the time values (startTime, frameDuration and duration) do not actually impact how long your test takes to execute, nor does it attach itself to the system clock. It is simply a way for you to have control over the first argument (currentTime) to requestAnimationFrame callbacks.

`createStub()`

type signature

function createStub (frameDuration: number = 1000 / 60, startTime: number = performance.now()): Stub

Basic usage

const stub = createStub();

Advanced usage

const frameDuration = (1000 / 60) * 2; // an extra slow frame
const startTime = performance.now() + 1000;
const stub = createStub(frameDuration, startTime);

`stub.add(callback)`

It schedules the callback to be called in the next frame. It returns an id that can be used to cancel the frame in the future. Same api as requestAnimationFrame.

Callbacks will not automatically get called after a period of time. You need to explicitly release it using stub.step() or stub.flush()

type signature

function add (cb: Function): number

const stub = createStub();
const callback = () => {};

stub.add(callback);

`stub.remove(id)`

It takes the id of a stub.add() call and cancels it without calling it. Same api as cancelAnimationFrame(id).

type signature

function remove (id: number): void

const stub = createStub();
const callback = () => console.log('hi');

const id = stub.add(callback);

stub.remove(id);

// callback is not called as it is no longer queued
stub.step();

// *crickets*

`.step()`

Executes all callbacks in the current frame and optionally additional frames.

type signature

step: (steps?: number, duration?: ?number) => void

steps => the amount of animation frames you would like to release. Defaults to 1. This is useful when you have nested calls.
duration (Number) => the amount of time the frame takes to execute. The default duration value is provided by the frameDuration argument to createStub(frameDuration). However, you can override it for a specific .step() call using the duration argument.

Simple example

const callback1 = () => console.log('first callback');
const callback2 = () => console.log('second callback');
const stub = createStub();

stub.add(callback1);
stub.add(callback2);
stub.step();

// console.log => 'first callback'
// console.log => 'second callback'

Nested example

Some times calls to requestAnimationFrame themselves call requestAnimationFrame. step() will let you step through them one at a time.

// this example will use the 'replaceRaf' syntax as it is a little clearer
const callback = () => {
  console.log('first callback');

  // second frame
  requestAnimationFrame(() => console.log('second callback'));
};

requestAnimationFrame(callback);

// release the first frame
requestAnimationFrame.step();

// console.log => 'first callback'

// release the second frame
requestAnimationFrame.step();

// console.log => 'second callback'

Time manipulated example

const startTime = performance.now();
const frameDuration = 10;
const longFrameDuration = frameDuration * 2;
const stub = createStub(frameDuration, startTime);
const callback = currentTime =>
  console.log(`call time: ${startTime - currentTime}`);

stub.add(callback);
stub.step(1, longFrameDuration);

// console.log => call time: 20

`stub.flush()`

Executes all requestAnimationFrame callbacks, including nested calls. It will keep executing frames until there are no frames left. An easy way to to think of this function is "step() until there are no more steps left.

type signature

flush: (duration: ?number) => void

duration => the duration for each frame in the flush - each frame gets the same value. If you want different frames to get different values then use .step(). The default duration value is provided by the frameDuration argument to createStub(frameDuration). However, you can override it for a specific .flush() call using the duration argument.

Warning if your code just calls requestAnimationFrame in an infinite loop then this will never end. Consider using .step() for this use case

Simple example

// this example will use the 'replaceRaf' syntax as it is a little clearer

const callback = () => {
  console.log('first callback');

  // second frame
  requestAnimationFrame(() => console.log('second callback'));
};

requestAnimationFrame(callback);
api.flush();

// console.log => 'first callback'
// console.log => 'second callback'

Time manipulated example

const startTime = performance.now();
const stub = createStub(100, startTime);
const callback = currentTime =>
  console.log(`call time: ${currentTime - startTime}`);

stub.add(callback);
stub.flush(200);

// console.log => 'call time: 200'

`.reset()`

Clears all the frames without executing any callbacks, unlike flush() which executes all the callbacks. Reverts the stub to it's initial state. This is similar to remove(id) but it does not require an id; reset will also clear all callbacks in the frame whereas remove(id) only removes a single one.

type signature

reset: () => void

const callback = () => console.log('first callback');

requestAnimationFrame(callback);
api.reset();

// callback has been removed so this will do nothing
api.step();

// *crickets*

replaceRaf

`replaceRaf()`

This function is used to set overwrite requestAnimationFrame and cancelAnimationFrame on a root (eg window). This is useful if you want to control requestAnimationFrame for dependencies.

type signature

type ReplaceRafOptions = {
    frameDuration?: number,
    startTime?: number
};

function replaceRaf(roots?: Object[], options?: ?ReplaceRafOptions): void;

roots => an optional array of roots to be stubbed (eg [window, global]). If no root is provided then the function will automatically figure out whether to use window or global
options => optional additional values to control the stub. These values are passed as the frameDuration and startTime arguments to createStub()

options

startTime => see createStub()
frameDuration => see createStub()

Basic usage

import { replaceRaf } from 'raf-stub';

const root = {}; // could be window, global etc.
replaceRaf([root]);

// can let multiple roots share the one stub
// useful for when you testing environment uses `global`
// but some libraries may use `window`

replaceRaf([window, global]);

// if called with no arguments it will use 'window' in the browser and 'global' in node
replaceRaf();

// you can override the frameDuration and startTime for the stub
replaceRaf([window], {
  frameDuration: 200,
  startTime: performance.now() + 1000,
});

After calling replaceRaf a root it's requestAnimationFrame and cancelAnimationFrame functions have been set and given new capabilities.

// assuming running in node so 'global' is the global rather than 'window'
import { replaceRaf } from 'raf-stub';

replaceRaf(global);

const callback = () => alert('hi');

// existing browser api mapped to stub.add
const id = requestAnimationFrame(callback);

// existing browser api mapped to stub.remove
cancelAnimationFrame(id);

// step - see stub.step
requestAnimationFrame.step();

// flush - see stub.flush
requestAnimationFrame.flush();

// reset - see stub.reset
requestAnimationFrame.reset();

See stub for api documentation on step(), flush() and reset().

Disclaimers!

Each call to replaceRaf will add a new stub to the root. If you want to have the same stub on multiple roots then pass them in at the same time (eg replaceRaf([window, global])).
If you do a one time setup of replaceRaf() in a test setup file you will remember to clear the stub after each test.

requestAnimationFrame.reset();

ES5 / ES6

ES6 syntax:

import stub, { replaceRaf } from 'raf-stub';

ES5 syntax (compatible with node.js `require`);

var stub = require('raf-stub').default;
var replaceRaf = require('raf-stub').replaceRaf;

Flow types

This library uses and publishes flow types. This ensures internal API consistency and also provides a great consumption story. If your project is using flow types then you can get type checking for all of your raf-stub calls, as well as auto complete depending on your editor.

Semantic Versioning

This project used Semantic versioning 2.0.0 to ensure a consistent versioning strategy.

X.Y.Z (major, minor, patch)

X: breaking changes
Y: new features (non breaking)
Z: patches

A safe raf-stub package.json dependency would therefore be anything that allows changes to the minor or patch version

Frame `currentTime` precision warning

When you a frame is called by .step() or .flush() it is given the currentTime as the first argument.

const stub = createStub();
const callback = currentTime => console.log(`the time is ${currentTime}`);

stub.add(callback);
stub.step();

// console.log('the current time is 472759.63');

By default frameDuration is 1000 / 60 and startTime is performance.now. Both of these numbers are ugly decimals (eg 16.6666667). When they are added together in .step() or .flush() this can cause known precision issues in JavaScript. You can find some further discussion about it's impact here.

Work arounds If you want to assert the current time inside of a callback - be sure to add the expected time values:

const frameDuration = 1000 / 60;
const startTime = performance.now();
const stub = createStub(frameDuration, startTime);
const child = sinon.stub();
const parent = sinon.stub().returns(child);

stub.add(callback);
stub.step();
stub.step();

// okay
expect(parent.calledWith(startTime + frameDuration)).to.be.true;

// not okay - will not mimic precision issues
// doing this can lead to flakey tests
expect(child.calledWith(startTime + 2 * frameDuration)).to.be.true;

// okay
expect(child.calledWith(startTime + frameDuration + frameDuration));

Another simple option is to use integers for both frameDuration and startTime.

const frameDuration = 16;
const startTime = 100;
const stub = createStub(frameDuration, startTime);
const child = sinon.stub();
const parent = sinon.stub().returns(child);

stub.add(callback);
stub.step();
stub.step();

// okay
expect(parent.calledWith(startTime + frameDuration)).to.be.true;

// okay
expect(child.calledWith(startTime + 2 * frameDuration)).to.be.true;

// okay
expect(child.calledWith(startTime + frameDuration + frameDuration));

Recipes

`frameDuration` and `startTime`

The first argument to a requestAnimationFrame callback is a DOMHighResTimeStamp

requestAnimationFrame(currentTime => {
  console.log('the current time is', currentTime);
});

Under normal circumstances you would not want to modify the default values. Being able to manipulate the startTime and endTime will let you test code that does some logic based on the currentTime argument.

Note changing the time values does not actually impact how long your test takes to execute, nor does it attach itself to the system clock. It is simply a way for you to have control over the first argument (currentTime) to requestAnimationFrame callbacks.

const idealFrameDuration = 1000 / 2;
const slowFrameDuration = idealFrameDuration * 2;
const startTime = performance.now();
const stub = createStub(slowFrameDuration, startTime);

stub.add(currentTime => {
  if (startTime + currentTime > idealFrameDuration) {
    console.log('a slow frame occured');
  } else {
    console.log('a standard frame occured');
  }
});

stub.step();

// console.log => 'a slow frame occured'

Controlling the frameDuration and startTime:

const callback = currentTime =>
  console.log(`time taken: ${currentTime - startTime}`);

// this will set the frameDuration and startTime for all stub calls. They can be overwritted with specific function calls
const stub = createStub(100, performance.now());

stub.add(callback);
// this will use the values specific when creating the stub
stub.step();
// console.log => 'time taken: 100'

stub.add(callback);
// this will overwrite the duration of the frame to '200' for this call
stub.step(1, 200);
// console.log => 'time taken: 200'

stub.add(callback);
stub.flush();
// console.log => 'time taken: 100'

stub.add(callback);
stub.flush(200);
// console.log => 'time taken: 200'

Library dependency

Let's say you use a library that uses request animation frame

// library.js
const ponyfill = callback => setTimeout(callback, 1000 / 60);
const raf = requestAnimationFrame || ponyfill;

export default function() {
  raf(() => {
    console.log('render allthethings!');
  });
}

The trouble with this is that the library uses a local variable raf. This reference is declared when the modules are importing. This means that raf will always points to the reference it has when the module is imported for the first time.

The following will not work

// test.js
import createStub from 'raf-stub';
import render from 'library';

describe('app', () => {
  const stub = createStub();

  beforeEach(() => {
    sinon.stub(global, 'requestAnimationFrame', stub.add);
    sinon.stub(console, 'log');
  });

  it('should allow us to execute requestAnimationFrame when we want', () => {
    render();

    stub.step();

    // *crickets* - not executed! :(
    expect(console.log.called).to.be(true); // failure
  });
});

This won't work when:

requestAnimationFrame does exist

raf === requestAnimationFrame;

This is because doing sinon.stub(global, 'requestAnimationFrame', stub.add) will change the reference that requestAnimationFrame points to. What that means is that the library when it calls raf will call the original requestAnimationFrame and not your stub

requestAnimationFrame does not exist

raf === ponyfill;

If the ponyfill is being used then we cannot override the reference to raf as it is not exposed. Stubbing requestAnimationFrame will not help because the library uses a reference to the ponyfill.

How can we get this working?

replaceRaf to the rescue!

before any of your tests code is executed, including module imports, then take the opportunity to set up your stub!

// test-setup.js
// your test setup will be running before babel so I will write valid node code.
var createStub = require('raf-stub').default;

// option 1: setup a stub yourself
var stub = createStub();
requestAnimationFrame = stub.add;
requestAnimationFrame = stub.remove;

// add additional helpers to requestAnimationFrame:
Object.assign(requestAnimationFrame, {
  step: stub.step,
  flush: stub.flush,
  reset: stub.reset,
});

// option 2: use replaceRaf! (this does option1 for you)
require('raf-stub').replaceRaf();

Then everything will work as expected!

// test.js
import render from 'library';

describe('app', () => {
  const stub = createStub();

  afterEach(() => {
    requestAnimationFrame.reset();
  });

  it('should allow us to execute requestAnimationFrame when we want', () => {
    render();

    requestAnimationFrame.step();

    // console.log => 'render allthethings!'
    expect(console.log.called).to.be(true);
  });
});

Full `mocha` end-to-end setup

For when you need to make a stub which can be used by a library (or module that ponyfills requestAnimationFrame at compile time)

package.json

{
  "scripts": {
    "test": "mocha render.test.js --presets es2015 --require test-setup.js"
  }
}

mocha test.js our test file
--presets es2015 this will let us use es6 + es6 modules in our test files
--require test-setup.js this is our file where we will setup our stub

test-setup.js

// using node require as the babel tranform is not applied to this file
require('raf-stub').replaceRaf();

render.js

const ponyfill = callback => setTimeout(callback, 1000 / 60);
const raf = requestAnimationFrame || ponyfill;

export default function() {
  raf(() => console.log('done'));
}

render.test.js

import render from './render';

describe('render', () => {
  it('should log to the console', () => {
    render();

    requestAnimationFrame.step();

    // console.log => 'done';
    expect(console.log.called).to.be(true);
  });
});

command line

npm test

Tests for `raf-stub`

To run the tests for this library simply execute:

npm install
npm test

Rationale for library

Let's say you wanted to test some code that uses requestAnimationFrame. How would you do it? Here is an example that uses sinon and setTimeout. You do not need to use sinon but it lets you write sequential code rather than needing to use nested timeouts.

describe('app', () => {
  let clock;

  beforeEach(() => {
    clock = sinon.useFakeTimers();
    sinon.stub(window, 'requestAnimationFrame', setTimeout);
    sinon.stub(window, 'cancelAnimationFrame', clearTimeout);
  });

  afterEach(() => {
    clock.restore();
    window.requestAnimationFrame.restore();
    window.cancelAnimationFrame.restore();
  });

  it('should allow us to execute requestAnimationFrame when we want', () => {
    const callback = () => console.log('success');

    requestAnimationFrame(callback);

    // fast forward set timeout
    clock.tick();

    // console.log => 'success'
    expect(console.log.called).to.be(true);
  });
});

We are all good right? Well sort of. For this basic example setTimeout was sufficient. Let's have a look at a few more cases where setTimeout is not ideal.

The following examples will assume the same setup as the above example unless otherwise specified

Case 1: mixture of `setTimeout` and `requestAnimationFrame`

it('should allow us to execute requestAnimationFrame when we want', () => {
  const callback = () => {
    setTimeout(() => {
      console.log('success');
    });
  };

  requestAnimationFrame(callback);

  // fast forward requestAnimationFrame
  clock.tick();

  // fast forward setTimeout
  clock.tick();

  // console.log => 'success'
  expect(console.log.called).to.be(true);
});

Because both setTimeout and requestAnimationFrame use setTimeout the way we step through an animation frame is the same way we step through a timeout. This can become hard to reason about in larger functions where there may be a large combination of setTimeout and requestAnimationFrame code. Having a shared mechanism is prone to misunderstandings. This is solved by stub.step() and stub.flush()

Case 2: nested requestAnimationFrames

it('should allow us to execute requestAnimationFrame when we want', () => {
  const callback = () => {
    requestAnimationFrame(() => {
      console.log('success');
    });
  };

  requestAnimationFrame(callback);

  // fast forward requestAnimationFrame
  clock.tick();

  // fast forward requestAnimationFrame
  clock.tick();

  // console.log => 'success'
  expect(console.log.called).to.be(true);
});

This was not too hard. But something to notice is that the nest code is identicial to the previous example. We are relying on comments to understand what is going on.

Let's go a bit deeper:

it('should allow us to execute requestAnimationFrame when we want', () => {
  const render = (iterations = 0) => {
    if (iterations > 100 * Math.random()) {
      return console.log('done');
    }
    return requestAnimationFrame(() => {
      render(iterations + 1);
    });
  };

  render();

  // step through the animation frames
  clock.tick(100000);

  // console.log => 'success'
  expect(console.log.called).to.be(true);
});

The problem we have here is that we do not know exactly how many times render will call requestAnimationFrame. To get around this we just tick the clock forward some really large amount. This feels like a hack. Also, you might use a number that is big enough in some circumstances but not others. This can lead to flakey tests. This is solved by stub.flush()

Case 3: `setTimeout` leakage

it('should log to the console', () => {
  const callback = () => {
    console.log('test 1: first frame');
    // requests another frame
    requestAnimationFrame(() => {
      console.log('test 1: second frame');
    });
  };

  requestAnimationFrame(callback);
  clock.tick();

  // console.log => 'test 1: first frame'
  expect(console.log.calledOnce).to.be(true);
  // note the second frame was not cleared
});

it('should also log to the console', () => {
  const callback = () => console.log('test 2: first frame');

  requestAnimationFrame(callback);
  clock.tick();

  // console.log => 'test 1: second frame' -> leaked from first test
  // console.log => 'test 2: first frame'
  expect(console.log.calledOnce).to.be(true); // failure
});

What happened here? We did not clear out all of therequestAnimationFrame's in the original test and they leaked into our second test. We need to reset the setTimeout queue before running test 2.

describe('app', () => {
  let clock;

  beforeEach(() => {
    clock = sinon.useFakeTimers();
    sinon.stub(window, 'requestAnimationFrame', setTimeout);
    sinon.stub(window, 'cancelAnimationFrame', clearTimeout);
  });

  afterEach(() => {
    // need to reset the clock (this actually flushes the clock)
    clock.tick(1000000);

    // console.log => 'test 1: second frame'

    clock.restore();
    window.requestAnimationFrame.restore();
    window.cancelAnimationFrame.restore();
  });

  it('test 1', () => {
    const callback = () => {
      console.log('test 1: first frame');
      requestAnimationFrame(() => {
        console.log('test 1: second frame');
      });
    };

    requestAnimationFrame(callback);

    // console.log => 'test 1: first frame'
    expect(console.log.called).to.be(true);

    // note the second frame was not cleared
  });

  it('test 2', () => {
    const callback = () => console.log('test 2: first frame');

    requestAnimationFrame(callback);

    // console.log => 'test 1: second frame'
    expect(console.log.calledOnce).to.be(true); // now passing
  });
});

We got around this issue by flushing the clock. We did this by calling clock.tick(some big number). This suffers from the problem that existed a previous example: you cannot be sure that you have actually emptied the queue. You might have noticed a strange console.log in the afterEach function. This is because when you emptied the setTimeout queue with clock.tick all of the callbacks executed. In some cases it might lead to unintended consequences. stub.reset() allows us to empty a queue without needing to execute any of the callbacks.

Case 4: controlling the first argument to `requestAnimationFrame` callbacks

Lets say you have setup that looks like this:

const idealFrameDuration = 1000 / 60;

const startAnimation = startTime => {
  let previousTime = startTime;

  const loop = currentTime => {
    if (!currentTime) {
      throw new Error('could not get the current time');
    }

    const diff = currentTime - previousTime;
    if (diff > idealFrameDuration) {
      console.log('a slow frame occurred');
    } else {
      console.log('a normal frame occurred');
    }

    previousTime = currentTime;
    requestAnimationFrame(loop);
  };

  requestAnimationFrame(loop);
};

startAnimation(performance.now());

How could we test the behaviour of the loop function? Let's try with setTimeout

describe('startAnimation', () => {
  let clock;

  beforeEach(() => {
    clock = sinon.useFakeTimers();
    sinon.stub(window, 'requestAnimationFrame', setTimeout);
    sinon.stub(window, 'cancelAnimationFrame', clearTimeout);
  });

  afterEach(() => {
    clock.restore();
    window.requestAnimationFrame.restore();
    window.cancelAnimationFrame.restore();
  });

  it('should pass the updated time to loop', () => {
    const startTime = performance.now();
    startAnimation(startTime);

    clock.tick();

    // Error => 'could not get the current time'
  });
});

What happened here? By default setTimeout does not pass any argument as the first parameter to callbacks. Getting this to work is hard because we would need to both use setTimeout as a replacement for requestAnimationFrame as well as changing it's behaviour to pass a controlled value as the first argument.

How can raf-stub help us?

import { replaceRaf } from 'raf-stub';
const startTime = performance.now();
const idealFrameDuration = 1000 / 60;

replaceRaf([], { startTime });

describe('startAnimation', () => {
  afterEach(() => {
    requestAnimationFrame.reset();
  });

  it('should pass the updated time to loop', () => {
    const slowFrameDuration = idealFrameDuration * 2;
    startAnimation(startTime);

    requestAnimationFrame.step(1, idealFrameDuration);
    // console.log => 'a normal frame occurred'
    expect(console.log.calledOnce).to.be(true);

    requestAnimationFrame.step(1, slowFrameDuration);
    // console.log => 'a slow frame occurred'
    expect(console.log.calledTwice).to.be(true);
  });
});

Name		Name	Last commit message	Last commit date
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flow-typed/npm		flow-typed/npm
src		src
test		test
.babelrc		.babelrc
.browserlistrc		.browserlistrc
.eslintrc.js		.eslintrc.js
.flowconfig		.flowconfig
.gitignore		.gitignore
.nvmrc		.nvmrc
.prettierignore		.prettierignore
.prettierrc		.prettierrc
.travis.yml		.travis.yml
LICENSE		LICENSE
README.md		README.md
package.json		package.json
rollup.config.js		rollup.config.js
yarn.lock		yarn.lock

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raf-stub

Basic usage

Replace existing requestAnimationFrame

Installation

stub

createStub()

stub.add(callback)

stub.remove(id)

.step()

stub.flush()

.reset()

replaceRaf

replaceRaf()

Basic usage

Disclaimers!

ES5 / ES6

ES6 syntax:

ES5 syntax (compatible with node.js require);

Flow types

Semantic Versioning

Frame currentTime precision warning

Recipes

frameDuration and startTime

Library dependency

How can we get this working?

Full mocha end-to-end setup

Tests for raf-stub

Rationale for library

Case 1: mixture of setTimeout and requestAnimationFrame

Case 2: nested requestAnimationFrames

Case 3: setTimeout leakage

Case 4: controlling the first argument to requestAnimationFrame callbacks

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Replace existing `requestAnimationFrame`

`createStub()`

`stub.add(callback)`

`stub.remove(id)`

`.step()`

`stub.flush()`

`.reset()`

`replaceRaf()`

ES5 syntax (compatible with node.js `require`);

Frame `currentTime` precision warning

`frameDuration` and `startTime`

Full `mocha` end-to-end setup

Tests for `raf-stub`

Case 1: mixture of `setTimeout` and `requestAnimationFrame`

Case 3: `setTimeout` leakage

Case 4: controlling the first argument to `requestAnimationFrame` callbacks

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