There are 2 main problems in generative testing:

- Input data generation (how do you explore enough of the program's behavior to have confidence that you're test is a good proxy for total correctness)

- Correctness statements (how do you express whether or not the program is correct for an arbitrary input)

When you are porting a program, you have a built in correctness statement: The port should behave exactly as the source program does. This greatly simplifies the testing process.