Test Eclipse JDT refactoring

What is the best way to unit test a JDT Eclipse plugin which performs LTK refactorings? Do any helper classes exist for this purpose?

My plugin contains a class which extends org.eclipse.ltk.core.refactoring.Refactoring and implements the methods checkInitialConditions(...), checkFinalConditions(...) and createChange(...). Moreover, I have classes implementing RefactoringContribution and RefactoringDescriptor.

However, I don't know where my tests should hook in. How can I start the refactoring from the code?