You are responsible for the integration testing of a system that encrypts network traffic. This system includes a key generator subsystem that uses random numbers. During integration testing, you use a stub implementation of the key generator that produces a predictable result. However, for the release version of the system, you want to substitute the stub implementation with the random implementation, so that the generated keys are not predictable to an outsider. Implement a test infrastructure using one of the design patterns described in Chapter 8, Object Design: Reusing Pattern Solutions to enable the exchange of these two key generator implementations at run time. Justify your choice.