OOS (Object-Oriented Systems) facilitate the change in the system in order to improve the functionality of the system. UML (Unified Modeling Language) as a standard as a standard of specification of object systems should be a natural source of information relevant to the testing. However, the systems are usually very complex. Moreover, the UML models contain a lot of data which are difficult for formalization and require human assistance. This makes ATPG (Automatic Test Pattern Generatio) from UML very doubtful. Consequently, random testing might be an interesting alternative for ATPG.