Teams that have embraced DevOps and begun using the practice of test driven development are familiar with the headaches that accompany testing legacy code.
This is particularly true for companies that have applications out in production that have been working for years, but have no formal tests or testing regiment associated with its codebase.
Most of the time the physical code for the applications is known; many times it is not. In fact, both the code and the developer who wrote the code might have left the building years ago.