Indentation works against `contains` test

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 (

)
}
}

expect().to.contain(

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

```
Test JSX output:
```

```
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.