Mutation testing is a fault-based technique. Mutation testing is performed at the final stage of the software, that is, before the delivery of the software to the customer. Mutation testing is a technique which measures the adequacy of a test case by seeding artificial defects(mutants) into a program. If a test case fails to detect a mutant, it may also fail to detect real faults or defects. A mutation over the original program may not change the semantics of the program; hence it is hard to detect the changes by a test case. This problem should be got rid of. There also exists another type of mutants which keep the program semantics unchanged and thus cannot be detected by any test case, this issue must be considered by generating more number of mutants. To deal with this problem, the authors introduce MUJAVA, by applying various mutations. MUJAVA supports two level mutant operators (Traditional mutation operators and class level mutation operators). For evaluating the effectiveness of the proposed methodology open source system will be considered and experiments will be implemented using MUJAVA testing tool.