Indentation works against `contains` test

[tomascasas]

I found myself testing a component with nested components which I decided to mock. The component also returns a "lot" of html. That is why I decided to test the component contains certain pieces instead of for equality.

This is a valid example of the issue:

class MyComponent extends Component {
  render({imgUrl}) {
    return (
      <div>
        <img src={imgUrl}/>
      </div>
    )
  }
}

expect(<MyComponent imgUrl="http://url" />).to.contain(
  <img src="http://url"/>
)

The test will fail due to rendering of MyComponent vs. the contained render indents differ. See:
MyComponent output:

<div>
  <img src="http://url"/>
  </img>
</div>

Test JSX output:

<img src="http://url"/>
</img>

I think the easiest fix is to prevent indentation when using contains test. Output will not look nice but would still allow to have the test passing.

[tomascasas]

I see the dependency to preact-render-to-string, and onRender opts should take care of that. Will report back.

[tomascasas]

Just went through code one more time and I realized it is pulling preact-render-to-string/jsx to render and that attributeHook function (default option) is the one introducing the \n that prevents from returning a single line output.
Can you help me understand why you use that import instead of the default preact-render-to-string?

[developit]

That import preserves component names and applies formatting to complex attribute values (prop values), including the ability to serialized JSX within props. I think we'll need to make the comparison in this repo intelligent enough to strip leading/trailing whitespace.

[tomascasas]

I'll see if I can help. Will go through preact-render-to-string/jsx/attributeHook again. Thanks!

[developit]

Ah actually it looks like this is a bug that was recently introduced in preact-render-to-string. The following condition turns <img></img> into <img /></img>, which is incorrect and breaks your comparison:
https://github.com/developit/preact-render-to-string/blob/master/src/index.js#L161-L163