GH-98831: Add some tests for generate_cases.py by gvanrossum · Pull Request #100763 · python/cpython

- This doesn't cover everything (far from it) but it's a start.
- This uses pytest, which isn't ideal, but was quickest to get started.

In anticipation of run_opcode_test().

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>