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https://github.com/mzgoddard/preact-render-spy

Render preact components with access to the produced virtual dom for testing.
https://github.com/mzgoddard/preact-render-spy

jsx preact test testing vdom

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Render preact components with access to the produced virtual dom for testing.

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README 

        
# preact-render-spy



preact-render-spy is a package designed to cover many of the use cases for testing

preact components.  The API is roughly modeled after enzyme, but we do not support

as many options currently.



[![Build Status](https://travis-ci.org/mzgoddard/preact-render-spy.svg?branch=master)](https://travis-ci.org/mzgoddard/preact-render-spy)



## Support:



We do our best to support Node.JS v6.11.0 and up, and speficially testing with jest, though other test runners should have no problems.



## Expressive Testing Example:



```jsx

import {h} from 'preact';

import {shallow} from 'preact-render-spy';

import Testable from './testable';



it('lets you do cool things with preact components', () => {

  const context = shallow();

  expect(context.find('div').contains(link)).toBeTruthy();

  context.find('[onClick]').simulate('click');

  expect(context.find('a').text()).toBe('clicked');

});

```



## How it works



The main render method takes some arbitrary JSX and replaces any component nodes with

spies which wrap the component.  These spies then look at the rendered output of the

second level of JSX and stores a big map of all the JSX virtual DOM nodes that have

been created by your component.



There is also concept of limiting the `depth` of the rendering such that it will only resolve

a certain number of levels deep in the component tree.  The `depth` of the default renderer

is set to `Infinity`, and we provide another renderer called `shallow` to render with

`{ depth: 1 }`.



## Jest Snapshot support

We provide a plugin for rendering your jsx snapshots to a formatted string that you can enable

using the jest configuration:



```json

{

  "snapshotSerializers": [ "preact-render-spy/snapshot" ]

}

```



## Configuration

We export a `config` object which you can use to change some of the internal options.

The values shown in this section are the defaults:



```js

import {config} from 'preact-render-spy';



// This property is used by the spy renderer to pass information to the spies about where

// they are in the vdom tree, it is generally removed from the properties passed down to your

// component, but it might show up in some cases, and we want you to be able to pick it.

config.SPY_PRIVATE_KEY = 'SPY_PRIVATE_KEY';



// These options are passed to preact-render-to-string/jsx whenever you snapshot a VNode or

// FindWrapper (and on the FindWrapper's toString method)

config.toStringOptions = { shallow: true, skipFalseAttributes: false };



// This option allows you to use a custom DOM implementation instead of relying on a global

// document.createDocumentFragment()

config.createFragment = () => document.createDocumentFragment();

```



## Exported Methods



### `deep(jsx, {depth = Infinity} = {})`

Creates a new `RenderContext` and renders using `opts.depth` to specify how many components deep

it should allow the renderer to render.  Also exported as `render` and `default`.



Example:

```jsx

const Deeper = () => 
Until Infinity!
;

const Second = () => ;

const First = () => ;



let context;

context = deep();

expect(context.find('div').text()).toBe('Until Infinity!');



context = deep(, { depth: 2 });

// We rendered First and Second, but not Deeper, so we never render a 


expect(context.find('div').length).toBe(0);

```



### `shallow(jsx)`

Creates a new `RenderContext` with `{ depth: 1 }`.



### `RenderContext#find(selector)`

Given a rendered context, `find` accepts a "css like" language of selectors to search through the

rendered vdom for given nodes.  **NOTE:** We only support this very limited set of "selectors", and no nesting.

We may expand this selector language in future versions, but it acheives our goals so far!



* `find('.selector')` - searches for any nodes with `class` or `className` attribute that matches `selector`

* `find('#selector')` - searches for any nodes with an `id` attribute that matches `selector`

* `find('[selector]')` - searches for any nodes which have an attribute named `selector`

* `find('Selector')` - searches for any nodes which have a nodeName that matches `Selector`,

  this will search for function/classes whos `name` is `Selector`, or `displayName` is `Selector`.

  If the `Selector` starts with a lower case letter, it will also check for tags like `div`.

* `find()` - searches for any nodes whos nodeName equals `Selector`

  and attributes match the ones given in the JSX.  **NOTE:** This does not support children, just simple attributes.

  Can be useful to find components from minified output that don't include display names.

  `.find()` will look for JSX nodes using the same `ImportedComponent` function.



This will return you a [`FindWrapper`](#findwrapper) which has other useful methods for testing.



### `RenderContext` extends `FindWrapper`



Like [`#find(selector)`](#rendercontextfindselector) `RenderContext` has the rest of `FindWrapper`'s methods.



### `RenderContext#render(jsx)`

Renders the root level jsx node using the same depth initially requested.  This can be useful for testing

`componentWillReceiveProps` hooks.



Example:



```jsx

const Node = ({name}) => 
{name}


const context = shallow();

expect(context.find('div').text()).toBe('example');



context.render();

expect(context.find('div').text()).toBe('second');

```



### `RenderContext.rerender()`

Calls `preact.rerender()` which performs any state changes in the render queue.



### `FindWrapper`

Contains a selection of nodes from `RenderContext#find(selector)`.

Has numeric indexed properties and length like an array.



### `FindWrapper#at(index)`

Returns another `FindWrapper` at the specific index in the selection.  Similar to `wrapper[0]` but will

allow using other `FindWrapper` methods on the result.



### `FindWrapper#attr(name)`

Requires a single node selection to work.

Returns the value of the `name` attribute on the jsx node.



### `FindWrapper#attrs()`

Requires a single node selection to work.

Returns a copy of the attributes passed to the jsx node.



### `FindWrapper#component()`

Requires a single node, which is a class based component.

Returns the **Spied** component. preact-render-spy creates a subclass of your components that enable us to spy things, you'll get a `class Spy extends YourComponent` instance.



Example:

```jsx

const context = shallow();

expect(context.component()).toBeInstanceOf(MyComponent);

```



### `FindWrapper#contains(vdom)`

Searches for any children matching the vdom or text passed.



### `FindWrapper#children()`

Returns `FindWrapper` with children of current wrapper.



### `FindWrapper#childAt(index)`

Returns `FindWrapper` with child at given index.

This has the same effect as calling `wrapper.children().at(index)`.



```jsx

const context = shallow();

expect(context.childAt(1).text()).toBe('Second list element');

```



### `FindWrapper#exists()`

Returns whether or not given node exists.



### `FindWrapper#filter(selector)`

Returns a new `FindWrapper` with a subset of the previously selected elements given the selector argument.



Uses the same possible selectors as [`RenderContext#find(selector)`](#rendercontextfindselector).



### `FindWrapper#map(fn)`

Maps array of nodes from this `FindWrapper` to another array.

Each node is passed in as a `FindWrapper` to the map function along with index number of element.



```jsx

const context = shallow((

  
    

        
  • first
    • 

        
  • second
    • 

        
  • third
    • 

      


));



const items = context.find('.item').map(node => node.text());

expect(items).toEqual(['first', 'second', 'third']);

```



### `FindWrapper#find(selector)`

Selects descendents of the elements previously selected. Returns a new `FindWrapper` with the newly selected elements.



Uses the same possible selectors as [`RenderContext#find(selector)`](#rendercontextfindselector).



### `FindWrapper#first()`

Returns another `FindWrapper` at the first index in the selection.



### `FindWrapper#last()`

Returns another `FindWrapper` at the last index in the selection.



### `FindWrapper#setState(newState)`

Requires a single node, which is a class based component.

Allows you to set the state of a rendered component.  Automatically `rerender()`s the view.



Example:

```jsx

const context = shallow();

context.setState({ count: 2 });

expect(context.text()).toEqual('2');

```



### `FindWrapper#simulate(event, ...args)`

Looks for an attribute properly named `onEvent` or `onEventCapture` and calls it, passing the arguments.



### `FindWrapper#state(key)`

Requires a single node, which is a class based component.

Reads the current state from the component. When passed `key`, this is essentially shorthand `state(key) === state()[key]`.



Example:

```jsx

const context = shallow();

expect(context.state()).toEqual({ count: 0 });

context.find('[onClick]').simulate('click');

expect(context.state('count')).toEqual(1);

```



### `FindWrapper#text()`

Returns the flattened string of any text children of any child component.



### `FindWrapper#output()`

Requires a single Component or functional node. Returns the vdom output of the given component.

Any Component or functional nodes will be "recursive" up to the depth you specified.  I.E.:



Example:

```jsx



const Second = ({ children }) => 
second {children}
;

const First = () => first;



// rendered deep, we get the div output

expect(deep().output()).toEqual(
second first
);

// rendered shallow, we get the  jsx node back

expect(shallow().output()).toEqual(first);

```



## Examples



There are many examples in the source files.  Some [tests specific to shallow](https://github.com/mzgoddard/preact-render-spy/blob/master/src/shallow-render.test.js), [tests specific to deep](https://github.com/mzgoddard/preact-render-spy/blob/master/src/deep-render.test.js), and many more [tests against both](https://github.com/mzgoddard/preact-render-spy/blob/master/src/shared-render.test.js).



### Simulate Clicks:

```jsx

class ClickCount extends Component {

  constructor(...args) {

    super(...args);



    this.state = {count: 0};

    this.onClick = this.onClick.bind(this);

  }



  onClick() {

    this.setState({count: this.state.count + 1});

  }



  render({}, {count}) {

    return 
{count}
;

  }

}

const context = shallow();

expect(context.find('div').contains('0')).toBeTruthy();

context.find('[onClick]').simulate('click');

expect(context.find('div').contains('1')).toBeTruthy();

```



### Testing componentWillUnmount



```jsx

import { h, Component } from 'preact';

import { shallow } from 'preact-render-spy';



class Unmount extends Component {



  componentWillUnmount() {

    this.props.onUnmount(this);

  }



  render() {

    return 
Unmount me
;

  }

}



it('triggers unmount', () => {

  const trigger = jest.fn();

  const context = shallow();

  expect(trigger).not.toHaveBeenCalled();



  // This will trigger the componentWillUnmount

  context.render(null);

  expect(trigger).toHaveBeenCalled();

});

```



### Testing componentWillReceiveProps



```jsx

import { h, Component } from 'preact';

import { shallow } from 'preact-render-spy';



class ReceivesProps extends Component {

  constructor(props) {

    this.state = { value: props.value };

  }



  componentWillReceiveProps({ value }) {

    if (value !== this.props.value) {

      this.setState({ value: `_${value}_` })

    }

  }



  render() {

    return 
{this.state.value}


  }

}



it('receives props', () => {

  const context = shallow();

  expect(context.text()).toBe('test');



  context.render();

  expect(context.text()).toBe('_second_');

});

```