failed components in the system. In large multiprocessors a circuit-level fault diagnosis is impractical, therefore system-level diagnosis considers only processor faults. Processors periodically execute tests on each other. If an error was detected, the diagnostic procedure identifies faulty units by analyzing the collection of the test results (called the syndrome). Once these units were identified, they are logically isolated and the system is reconfigured to continue the error-free

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... . Generalized test invalidation Fault-free tester units are assumed to test other units correctly (tests are assumed to be complete). Still, faulty testers may produce and distribute incorrect test results that do not reflect the real fault state of the tested unit. In other words, errors affect the validity of test outcomes. This effect, modelled by test invalidation, makes the decoding of the syndrome more difficult. The two most frequently used test invalidation models are the symmetric or PMC model [2] , and the asymmetric or BGM model[3]: