The author's differential testing (2.3M random battles) is great as final validation, but the real lesson here is that modular testing should happen during the port, not after.

1. Port tests first - they become your contract 2. Run unit tests per module before moving on - catches issues like the "two different move structures" early 3. Integration tests at boundaries before proceeding 4. E2e/differential testing as final validation

When you can't read the target language, your test suite is your only reliable feedback. The debugging time spent on integration issues would've been caught earlier with progressive testing.