"1 or 2 plan mode prompts" to fully describe a 30-sheet complicated doc suggests a massively higher level of granularity than Opus initial plans on existing codebases give me or a less-than-expected level of Excel craziness.
And the tooling harnesses have been telling the models to add testing to things they make for months now, so why's that impressive or suprising?
I was impressed because the prompt didn't ask it to do that. It doesn't normally add tests for me without asking, YMMV.
Did it build a test suite for the Excel side? A fuzzer or such?
It's the cross-concern interactions that still get me.
80% of what I think about these days when writing software is how to test more exhaustively without build times being absolute shit (and not necessarily actually being exhaustive anyway).