If 2 separate test (methods) in the JUnit suite of test, are using 2 different .dmn files, having however the same Namespace and Name, and both defining an ItemDefinition with a specified name, but different structure, the classloading will be confused (trying to access a method not belonging to the expected class). Trying to redefine the same class?

Can be replicated by checking out the branch and reverting commit https://github.com/kiegroup/drools/pull/2886/commits/cb216ac827ea5b51afc82f98161a95ea8391aa1c