Given the Commercial Federal strategy to replace rather than remediate, the core system testing for mission critical applications becomes especially critical. A mirror environment of both hardware and software has been established for testing. Each change made to the system is tested in the mirror environment first. The testing phases applied for each system includes a rigorous test, in isolation, at all levels of the hardware, from network layers and data link layers through the application layer and handling of the data. Passing the effectiveness test in isolation merely means, the system is eligible to pass on to the Y2K readiness integration-testing phase.