Nit, consistency: rather than using
```javascript
'styleSheets': [
{
  // …
}]
```
please do either
```javascript
'styleSheets': [
  {
    // …
  }
]
```
or if the array has only one element:
```javascript
'styleSheets': [{
  // …
}]
```

This applies to `cssRules` too, and more generally with most of this `testCases` object.