Add ReactTestRenderer documentations (#10692)

* Add ReactTestRenderer documentations

* Add TestRenderer documentations

* TestRenderer is not experiment

* Add a link for jsdom

* Use ES Modules syntax

* Twaek

* Add a Link component

* Use Jest assertions

* Move a documentation for createNodeMock to Idea section

* Renamed

* Tweak

* Rename

* More explicit

* Add a usecase for createNodeMock

Author: koba04

docs/_data/nav_docs.yml

@@ -75,3 +75,5 @@
       title: Test Utilities
     - id: shallow-renderer
       title: Shallow Renderer
+    - id: test-renderer
+      title: Test Renderer

docs/docs/reference-test-renderer.md

@@ -0,0 +1,283 @@
+---
+id: test-renderer
+title: Test Renderer
+permalink: docs/test-renderer.html
+layout: docs
+category: Reference
+---
+
+**Importing**
+
+```javascript
+import TestRenderer from 'react-test-renderer'; // ES6
+const TestRenderer = require('react-test-renderer'); // ES5 with npm
+```
+
+## Overview
+
+This package provides a React renderer that can be used to render React components to pure JavaScript objects, without depending on the DOM or a native mobile environment.
+
+Essentially, this package makes it easy to grab a snapshot of the platform view hierarchy (similar to a DOM tree) rendered by a React DOM or React Native component without using a browser or [jsdom](https://github.com/tmpvar/jsdom).
+
+Example:
+
+```javascript
+import TestRenderer from 'react-test-renderer';
+
+function Link(props) {
+  return <a href={props.page}>{props.children}</a>;
+}
+
+const testRenderer = TestRenderer.create(
+  <Link page="https://www.facebook.com/">Facebook</Link>
+);
+
+console.log(testRenderer.toJSON());
+// { type: 'a',
+//   props: { href: 'https://www.facebook.com/' },
+//   children: [ 'Facebook' ] }
+```
+
+You can use Jest's snapshot testing feature to automatically save a copy of the JSON tree to a file and check in your tests that it hasn't changed: [Learn more about it](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html).
+
+You can also traverse the output to find specific nodes and make assertions about them.
+
+```javascript
+import TestRenderer from 'react-test-renderer';
+
+function MyComponent() {
+  return (
+    <div>
+      <SubComponent foo="bar" />
+      <p className="my">Hello</p>
+    </div>
+  )
+}
+
+function SubComponent() {
+  return (
+    <p className="sub">Sub</p>
+  );
+}
+
+const testRenderer = TestRenderer.create(<MyComponent />);
+const testInstance = testRenderer.root;
+
+expect(testInstance.findByType(SubComponent).props.foo).toBe('bar');
+expect(testInstance.findByProps({className: "sub"}).children).toEqual(['Sub']);
+```
+
+### TestRenderer
+
+* [`TestRenderer.create()`](#TestRenderer.create)
+
+### TestRenderer instance
+
+* [`testRenderer.toJSON()`](#testRenderer.toJSON)
+* [`testRenderer.toTree()`](#testRenderer.toTree)
+* [`testRenderer.update()`](#testRenderer.update)
+* [`testRenderer.unmount()`](#testRenderer.unmount)
+* [`testRenderer.getInstance()`](#testRenderer.getInstance)
+* [`testRenderer.root`](#testRenderer.root)
+
+### TestInstance
+
+* [`testInstance.find()`](#testInstance.find)
+* [`testInstance.findByType()`](#testInstance.findByType)
+* [`testInstance.findByProps()`](#testInstance.findByProps)
+* [`testInstance.findAll()`](#testInstance.findAll)
+* [`testInstance.findAllByType()`](#testInstance.findAllByType)
+* [`testInstance.findAllByProps()`](#testInstance.findAllByProps)
+* [`testInstance.instance`](#testInstance.instance)
+* [`testInstance.type`](#testInstance.type)
+* [`testInstance.props`](#testInstance.props)
+* [`testInstance.parent`](#testInstance.parent)
+* [`testInstance.children`](#testInstance.children)
+
+## Reference
+
+### `TestRenderer.create()`
+
+```javascript
+TestRenderer.create(element, options);
+```
+
+Create a TestRenderer instance with a passed element, which has the following methods and properties.
+
+### `testRenderer.toJSON()`
+
+```javascript
+testRenderer.toJSON()
+```
+
+Return a JSON object representing the element.
+
+### `testRenderer.toTree()`
+
+```javascript
+testRenderer.toTree()
+```
+
+Return a tree object representing the element.
+
+### `testRenderer.update()`
+
+```javascript
+testRenderer.update(element)
+```
+
+Update the element with a passed element.
+
+### `testRenderer.unmount()`
+
+```javascript
+testRenderer.unmount()
+```
+
+Unmount the element from testRenderer.
+
+### `testRenderer.getInstance()`
+
+```javascript
+testRenderer.getInstance()
+```
+
+Return a root container instance.
+
+### `testRenderer.root`
+
+```javascript
+testRenderer.root
+```
+
+`root` is a testInstance, which has the following methods and properties.
+
+### `testInstance.find()`
+
+```javascript
+testInstance.find(test)
+```
+
+Find a descendant testInstance that `test(testInstance)` is `true`.
+
+### `testInstance.findByType()`
+
+```javascript
+testInstance.findByType(type)
+```
+
+Find a descendant testInstance that matches the provided type.
+
+### `testInstance.findByProps()`
+
+```javascript
+testInstance.findByProps(props)
+```
+
+Find a descendant testInstance that matches the provided props.
+
+### `testInstance.findAll()`
+
+```javascript
+testInstance.findAll(test)
+```
+
+Find all descendant testInstances that `test(testInstance)` is `true`.
+
+### `testInstance.findAllByType()`
+
+```javascript
+testInstance.findAllByType(type)
+```
+
+Find all descendant testInstances that matches the provided type.
+
+### `testInstance.findAllByProps()`
+
+```javascript
+testInstance.findAllByProps(props)
+```
+
+Find all descendant testInstances that matches the provided props.
+
+### `testInstance.instance`
+
+```javascript
+testInstance.instance
+```
+
+`instance` is a component instance of the testInstance.
+
+### `testInstance.type`
+
+```javascript
+testInstance.type
+```
+
+`type` is a Component type of the testInstance.
+
+### `testInstance.props`
+
+```javascript
+testInstance.props
+```
+
+`props` is a props object of the testInstance.
+
+### `testInstance.parent`
+
+```javascript
+testInstance.parent
+```
+
+`parent` is a parent testInstance.
+
+### `testInstance.children`
+
+```javascript
+testInstance.children
+```
+
+`children` is children of the testInstance.
+
+## Ideas
+
+You can pass `createNodeMock` function to `TestRenderer.create` as the option, which allows for custom mock refs.
+`createNodeMock` accepts the current element and should return a mock ref object.
+This is useful when you test a component rely on refs.
+
+```javascript
+import TestRenderer from 'react-test-renderer';
+
+class MyComponent extends React.Component {
+  constructor(props) {
+    super(props);
+    this.input = null;
+  }
+  componentDidMount() {
+    this.input.focus();
+  }
+  render() {
+    return <input type="text" ref={el => this.input = el} />
+  }
+}
+
+let focused = false;
+TestRenderer.create(
+  <MyComponent />,
+  {
+    createNodeMock: (element) => {
+      if (element.type === 'input') {
+        // mock a focus function
+        return {
+          focus: () => {
+            focused = true;
+          }
+        };
+      }
+      return null;
+    }
+  }
+);
+expect(focused).toBe(true);
+```