No matter how much experience an engineer has, or how many engineer works on the design of a processor or a microcontroller, we are human at the end, and it is possible to make mistakes. Before sending a processor design to production, how are they tested so the processor works correctly?
Are they designing the whole processor in FPGA? or is the whole design checked and debugged by software? (I am considering the complexity of x86 processors, ARM, PIC etc.). Thinking about 1970s with the design of 8086, they didn't have that much technology.