- 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.
Several times I've been involved in porting code. Eventually we reach a time where we are getting a lot of bug reports "didn't work, didn't work with the old system as well" which is to say we ported correctly, but the old system wasn't right either and we just hadn't tested it in that situation until the new system had the budget for exhaustive testing. (normally it worked at one point on the old system and got broke in some other update)
- 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.