Right, that method is pretty good at finding unintentional behavior changes in a refactor. It is not very well suited for showing that the program is correct which is probably what your parent meant.
That doesn't seem like the same problem at all. The problem here was reimplementing the program in another language, not doing that while at the same time identifying bugs in it.
Conversion of one program to another while preserving behavior is a problem much dumber programs (like compilers) solve all the time.
Conversion of one program to another while preserving behavior is a problem much dumber programs (like compilers) solve all the time.