fakes.md

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page	Fakes - Sinon.JS	fakes

Introduction

Fakes are a new concept to Sinon, simplifying and merging the concepts from spies and stubs.

A test fake is a Function that records arguments, return value, the value of this and exception thrown (if any) for all its calls.

Fakes can be created with or without behaviour.

All fakes are immutable: once created, their behaviour will not change.

Unlike sinon.spy and sinon.stub APIs, the sinon.fake API knows only how to create fakes, and doesn't concern itself with plugging them into the system under test. To plug the fakes into the system under test, you can use the sinon.replace* methods.

Creating a fake

// create a basic fake, with no behaviour
var fake = sinon.fake();

fake();

console.log(fake.callCount);
// 1

Fakes with behaviour

Fakes can be created with behaviour, which cannot be changed once the fake has been created.

sinon.fake.returns(value);

Creates a fake that returns the value argument

var fake = sinon.fake.returns('apple pie');

fake();
// apple pie

sinon.fake.throws(value);

Creates a fake that throws an Error with the provided value as the message property.

If an Error is passed as the value argument, then that will be the thrown value. If any other value is passed, then that will be used for the message property of the thrown Error.

var fake = sinon.fake.throws(new Error('not apple pie'));

fake();
// Error: not apple pie

sinon.fakes.resolves(value);

Creates a fake that returns a resolved Promise for the passed value.

sinon.fakes.rejects(value);

Creates a fake that returns a rejected Promise for the passed value.

If an Error is passed as the value argument, then that will be the value of the promise. If any other value is passed, then that will be used for the message property of the Error returned by the promise.

sinon.fake.yields(callback[, value1, ..., valueN]);

Creates a fake that calls the provided callback with the provided values.

var fake = sinon.fake.yields(console.log, 'hello world');

fake();
// hello world

sinon.fake.yieldsAsync(callback[, value1, ..., valueN]);

Creates a fake that calls the provided callback asynchronously with the provided values.

var fake = sinon.fake.yieldsAsync(console.log, 'hello world');

fake();
// hello world

sinon.fake(func);

Wraps an existing Function to record all interactions, while leaving it up to the func to provide the behaviour.

This is useful when complex behaviour not covered by the sinon.fake.* methods is required or when wrapping an existing function or method.

Adding the fake to the system under test

Unlike sinon.spy and sinon.stub, sinon.fake only knows about creating fakes, not about replacing properties in the system under test.

To replace a property, you can use the sinon.replace method.

var fake = sinon.fake.returns('42');

sinon.replace(console, 'log', fake);

console.log('apple pie');
// 42

When you want to restore the replaced properties, simply call the sinon.restore method.

// restores all replaced properties set by sinon methods (restore, spy, stub)
sinon.restore();