Tested FluentDOM\Query::registerNamespace() for DOMDocument on existing XPath instance
Tested: FluentDOM\Query::getIterator()
Fixed @covers annotations for FluentDOM\Query::offsetSet() and FluentDOM\Query::offsetUnset() tests
Tested: isset(FluentDOM\Query::$document) property
Tested: reading FluentDOM\Query::$data property
Tested: unsetting FluentDOM\Query properties
Tested: use applyNamespaces() on implicit created Document
Added some @covers annotations for private manipulation helper methods