Add basic tests for all classes

[oliverklee]

• ├── Comment
• │   └── Comment.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── CSSList
• │   ├── AtRuleBlockList.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── Document.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   └── KeyFrame.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── OutputFormat.php
• ├── OutputFormatter.php
• ├── Parser.php
• ├── Parsing
• │   ├── Anchor.php
  • superclasses, interfaces
• │   ├── OutputException.php
  • superclasses, interfaces
• │   ├── ParserState.php
• │   ├── SourceException.php
  • superclasses, interfaces
• │   ├── UnexpectedEOFException.php
  • superclasses, interfaces
• │   └── UnexpectedTokenException.php
  • superclasses, interfaces
• ├── Property
• │   ├── AtRule.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── Charset.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── CSSNamespace.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── Import.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── KeyframeSelector.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   └── Selector.php
  • superclasses, interfaces
  • accessors
  • rendering
  • isValid()
  • parsing
• ├── Rule
• │   └── Rule.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── RuleSet
• │   ├── AtRuleSet.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• │   ├── DeclarationBlock.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── Settings.php
• └── Value
• ├── CalcFunction.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── CalcRuleValueList.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── Color.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── CSSFunction.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── CSSString.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── LineName.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── RuleValueList.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── Size.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing
• ├── URL.php
  • superclasses, interfaces
  • accessors
  • rendering
  • parsing