callbacks are per-class and therefore static in the beginning
use single mocked servlet context instance in tests
Add getter methods to protected fields
remove shared state variable that can be passed as parameter
test for checking that @ClassRule works in Spock
refactor Junit3 fixture method handling to separate private inner class
extract method
Add RuleFactory & ClassRuleFactory handling to TestMixinTransformation
Spock needs FieldMetadata annotation for Rule/ClassRule fields
update test to use TestMixin annotation again
Add getters for protected fields in ControllerUnitTestMixin