Two methods must be applied. First, the simulator must conform to the system specification for the hardware. Every instruction that retires must behave exactly as the hardware expects, including every result, and every control register. Unit tests can be written for these individual cases and used to maintain the simulator. Next, real world programs and applications should be ported to run on the simulator. Instrumentation code can be added to provide some kind of checksum section to ensure that the simulator is outputting results the same as hardware.