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Use runkit snippets in fake documentation (#2381)
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srknzl committed Jun 8, 2021
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should have working firstArg property", function () {
it("should have working firstArg", function () {
const f = sinon.fake();
const date1 = new Date();
const date2 = new Date();
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should have working lastArg property", function () {
it("should have working lastArg", function () {
const f = sinon.fake();
const date1 = new Date();
const date2 = new Date();
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should have working lastArg property", function () {
it("should be able to be added to the system under test", function () {
const fake = sinon.fake.returns("42");

sinon.replace(console, "log", fake);
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should create a fake that 'returns' a value", function () {
it("should create a fake that 'returns'", function () {
const fake = sinon.fake.returns("apple pie");

assert.equals(fake(), "apple pie");
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should create a fake that 'throws' an Error", function () {
it("should create a fake that 'throws'", function () {
const fake = sinon.fake.throws(new Error("not apple pie"));

// Expected to throw an error with message 'not apple pie'
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Expand Up @@ -4,7 +4,7 @@ const referee = require("@sinonjs/referee");
const assert = referee.assert;

describe("FakeTest", function () {
it("should have working callback property", function () {
it("should have working callback", function () {
const f = sinon.fake();
const cb1 = function () {};
const cb2 = function () {};
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190 changes: 29 additions & 161 deletions docs/release-source/release/fakes.md
Expand Up @@ -2,6 +2,19 @@
layout: page
title: Fakes - Sinon.JS
breadcrumb: fakes
examples:
- fakes-1-using-fakes-instead-of-spies
- fakes-2-using-fakes-instead-of-stubs
- fakes-3-creating-without-behaviour
- fakes-4-creating-with-custom-behaviour
- fakes-5-returns
- fakes-6-throws
- fakes-7-yields
- fakes-8-yields-async
- fakes-9-callback
- fakes-10-firstArg
- fakes-11-lastArg
- fakes-12-adding-fake-to-system-under-test
---

### Introduction
Expand All @@ -24,66 +37,23 @@ The created `fake` `Function`, with or without behavior has the same API as a (`

#### Using fakes instead of spies

```js
var foo = {
bar: () => {
return "baz";
},
};
// wrap existing method without changing its behaviour
var fake = sinon.replace(foo, "bar", sinon.fake(foo.bar));

fake();
// baz

fake.callCount;
// 1
```
<div data-example-id="fakes-1-using-fakes-instead-of-spies"></div>

#### Using fakes instead of stubs

```js
var foo = {
bar: () => {
return "baz";
},
};
// replace method with a fake one
var fake = sinon.replace(foo, "bar", sinon.fake.returns("fake value"));

fake();
// fake value

fake.callCount;
// 1
```
<div data-example-id="fakes-2-using-fakes-instead-of-stubs"></div>

### Creating a fake

Create a `fake` `Function` with or without [behavior](#fakes-with-behavior). The created `Function` has the same API as a [`sinon.spy`][spies].

#### Creating a fake without behavior

```js
// create a basic fake, with no behavior
var fake = sinon.fake();

fake();
// undefined

fake.callCount;
// 1
```
<div data-example-id="fakes-3-creating-without-behaviour"></div>

#### Creating a fake with custom behaviour

```js
// create a fake that returns the text "foo"
var fake = sinon.fake.returns("foo");

fake();
// foo
```
<div data-example-id="fakes-4-creating-with-custom-behaviour"></div>

### Fakes with behavior

Expand All @@ -93,25 +63,15 @@ Fakes cannot change once created with behaviour.

Creates a fake that returns the `value` argument.

```js
var fake = sinon.fake.returns("apple pie");

fake();
// apple pie
```
<div data-example-id="fakes-5-returns"></div>

#### `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`.

```js
var fake = sinon.fake.throws(new Error("not apple pie"));

fake();
// Error: not apple pie
```
<div data-example-id="fakes-6-throws"></div>

#### `sinon.fake.resolves(value);`

Expand All @@ -129,33 +89,15 @@ If an `Error` is passed as the `value` argument, then that will be the value of

In code example below, the '[readFile](https://nodejs.org/api/fs.html#fs_fs_readfile_path_options_callback)' function of the 'fs' module is replaced with a fake function created by `sinon.fake.yields`. When the fake function is called, it always calls the last argument it received, which is expected to be a callback, with the values that the `yields` function previously took.

```js
var fake = sinon.fake.yields(null, "file content");
sinon.replace(fs, "readFile", fake);
fs.readFile("somefile", (err, data) => {
console.log(data);
});
console.log("end of this event loop");
// file content
// end of this event loop
```
<div data-example-id="fakes-7-yields"></div>

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

Similar to `yields`, `yieldsAsync` also returns a function that when invoked, the function expects the last argument to be a callback and invokes that callback with the same previously given values. However, the returned function invokes that callback asynchronously rather than immediately, i.e. in the next event loop.

Compare the output of the code example below with the output of the code example above for `yields` to see the difference.
Compare the code example below with the code example above for `yields` to see the difference.

```js
var fakeAsync = sinon.fake.yieldsAsync(null, "file content");
sinon.replace(fs, "readFile", fakeAsync);
fs.readFile("somefile", (err, data) => {
console.log(data);
});
console.log("end of this event loop");
// end of this event loop
// file content
```
<div data-example-id="fakes-8-yields-async"></div>

#### `sinon.fake(func);`

Expand All @@ -172,106 +114,32 @@ The instance properties are the same as those of a [`sinon.spy`][spies]. The fol
#### `f.callback`

This property is a convenience to get a reference to the last callback passed in the last to the fake.
The same convenience has been added to [spy calls](../spy-call#spycallcallback).

```js
var f = sinon.fake();
var cb1 = function () {};
var cb2 = function () {};

f(1, 2, 3, cb1);
f(1, 2, 3, cb2);

f.callback === cb2;
// true
```

The same convenience has been added to [spy calls](../spy-call#spycallcallback):

```js
f.getCall(1).callback === cb2;
// true
//
f.lastCall.callback === cb2;
// true
```
<div data-example-id="fakes-9-callback"></div>

#### `f.firstArg`

This property is a convenient way to get a reference to the first argument passed in the last call to the fake.
The same convenience has been added to [spy calls](../spy-call#spycallfirstarg).

```js
var f = sinon.fake();
var date1 = new Date();
var date2 = new Date();

f(date1, 1, 2);
f(date2, 1, 2);

f.firstArg === date2;
// true
```

The same convenience has been added to [spy calls](../spy-call#spycallfirstarg):

```js
f.getCall(0).firstArg === date1;
// true
f.getCall(1).firstArg === date2;
// true
//
f.lastCall.firstArg === date2;
// true
```
<div data-example-id="fakes-10-firstArg"></div>

#### `f.lastArg`

This property is a convenient way to get a reference to the last argument passed in the last call to the fake.
The same convenience has been added to [spy calls](../spy-call#spycalllastarg).

```js
var f = sinon.fake();
var date1 = new Date();
var date2 = new Date();

f(1, 2, date1);
f(1, 2, date2);

f.lastArg === date2;
// true
```

The same convenience has been added to [spy calls](../spy-call#spycalllastarg):

```js
f.getCall(0).lastArg === date1;
// true
f.getCall(1).lastArg === date2;
// true

f.lastCall.lastArg === date2;
// true
```
<div data-example-id="fakes-11-lastArg"></div>

### 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`](../sandbox/#sandboxreplaceobject-property-replacement) method.

```js
var fake = sinon.fake.returns("42");

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

console.log("apple pie");
// 42
```

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

```js
// restores all replaced properties set by sinon methods (replace, spy, stub)
sinon.restore();
```
<div data-example-id="fakes-12-adding-fake-to-system-under-test"></div>

[spies]: ../spies
[stubs]: ../stubs

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