In an embodiment, a processor includes at least one core, a power management unit having a first test register including a first field to store a test patch identifier associated with a test patch and a second field to store a test mode indicator to request a core functionality test, and a microcode storage to store microcode to be executed by the at least one core. Responsive to the test patch identifier, the microcode may access a firmware interface table and obtain the test patch from a non-volatile storage according to an address obtained from the firmware interface table. Other embodiments are described and claimed.