Adding Plugins Guide

.gitignore

@@ -8,4 +8,6 @@ logs
 *.log
 npm-debug.log*
 yarn-debug.log*
-yarn-error.log*
+yarn-error.log*
+
+.idea

src/.vuepress/config.js

@@ -6,7 +6,8 @@ const sidebar = {
       children: [
         '/guide/installation',
         '/guide/introduction',
-        '/guide/a-crash-course'
+        '/guide/a-crash-course',
+        '/guide/plugins'
       ]
     },
     {

src/guide/a-crash-course.md

@@ -1,6 +1,7 @@
 # A Crash Course
 
-Let's jump write into it, and learn Vue Test Utils (VTU) by building a simple Todo app, and writing tests as we go. This guide will cover:
+Let's jump right into it, and learn Vue Test Utils (VTU) by building a simple Todo app, and writing tests as we go. This
+ guide will cover:
 
 - mounting components
 - finding elements

src/guide/plugins.md

@@ -0,0 +1,84 @@
+## Plugins
+
+Plugins add global-level functionality to Vue Test Utils' API. This is the
+ official way to extend Vue Test Utils' API with custom logic, methods, or
+   functionality.
+
+ If you're missing a bit of functionality, consider writing a plugin to
+  extend Vue Test Utils' API.
+
+ Some use cases for plugins:
+ 1. Aliasing existing public methods
+ 1. Attaching matchers to the Wrapper instance
+ 1. Attaching functionality to the Wrapper
+
+## Using a plugin
+
+Install plugins by calling the `config.plugins.VueWrapper.install()`  method
+. This has to be done before you call `mount`.
+
+ The `install()` method will receive an instance of `WrapperAPI` containing both
+  public and private properties of the instance.
+
+ ```js
+// setup.js file
+import { config } from '@vue/test-utils'
+
+// locally defined plugin, see "Writing a Plugin"
+import MyPlugin from './myPlugin'
+
+// Install a plugin onto VueWrapper
+config.plugins.VueWrapper.install(MyPlugin)
+```
+
+You can optionally pass in some options:
+```js
+config.plugins.VueWrapper.install(MyPlugin, { someOption: true })
+```
+
+Your plugin should be installed once. In Jest, this should be in your Jest
+ config's `setupFiles` or `setupFilesAfterEnv` file.
+
+Some plugins automatically call `config.plugins.VueWrapper.install()` when
+ they're imported. This is common if they're extending multiple interfaces at
+  once. Follow the instructions of the plugin you're installing.
+
+Check out the [Vue Community Guide](https://vue-community.org/guide/ecosystem
+/testing.html) or [awesome-vue](https://github.com/vuejs/awesome-vue#test
+) for a collection of community-contributed plugins and libraries.
+
+## Writing a Plugin
+
+A Vue Test Utils plugin is simply a function that receives the mounted
+ `VueWrapper` or `DomWrapper` instance and can modify it.
+
+Below is a simple plugin to add a convenient alias to map `wrapper.element` to `wrapper.$el`
+
+```js
+// setup.js
+import { config } from '@vue/test-utils'
+
+const myAliasPlugin = (wrapper) => {
+  return {
+    $el: wrapper.element // simple aliases
+  }
+}
+
+// Call install on the type you want to extend
+// You can write a plugin for any value inside of config.plugins
+config.plugins.VueWrapper.install(myAliasPlugin)
+```
+
+And in your spec, you'll be able to use your plugin after `mount`.
+```js
+// component.spec.js
+const wrapper = mount({ template: `<h1>🔌 Plugin</h1>` })
+console.log(wrapper.$el.innerHTML) // 🔌 Plugin
+```
+
+## Featuring your Plugin
+
+If you're missing functionality, consider writing a plugin to extend Vue Test
+ Utils and submit it to be featured at [Vue Community Guide](https://vue
+ -community.org/guide/ecosystem/testing.html) or [awesome-vue](https
+ ://github.com/vuejs/awesome-vue#test)