Implemented TestFest 'Descriptor\Validator' case
- Added PHPUnit test for Descriptor\Validator\Error at the TestFest
- Added docblocks for Descriptor\Validator\Error
- Fixed typo in Descriptor/CollectionTest
Forgot trailing newline
Merge pull request #1358 from dennisdegreef/descriptorValidatorTest

Implemented TestFest 'Descriptor\Validator' case