The tests can fail based on the execution order of these tests.

If PersistenceDbServiceTest is executed first then it sets session factory to MockSessionFactory.
Unfortunately it seems that the setting is SAME for ALL future newly created JbpmContexts.
PersistenceServiceDbTest then tests that the factory is null but it is not assertNull(persistenceServiceFactory.sessionFactory). The same test also tests few more features that ends in calls of unsupported operations on the MockSessionFactory.

I am not sure if this is a problem of test - then the sessionFactory should be cleard after test or if it is wrong that the setting is shared for all JBpmContexts.