I've set permissions of the existing unit tests to read-only for this reason, since I've seen all the recent Opus do this.
Sometimes it will also not careif a unit test fails, calling it "errant" or "legacy" or something, where it then removes it from the list (not sure how to get around that one, other than a read only launcher).
I found it eagerly reversing existing product decisions like changing a user given date into created date, since it thought creating something that is in the past is incorrect. This was not even related to the task at hand at all. I noticed this kind of stuff happens more with ultracode for some reason.
A change can introduce regressions in any large project even if 100% of unit tests pass. Unit tests test individual units, regressions can happen at many levels. Especially if we treat performance degradations as regressions.
I detect the regression already in planning with Opus 5, so I do not let Opus 5 implement anything. But it is a waste of time and tokens! Does planning with Opus 5 works out for you?
It sounds like you just need to correct the plan it lays out to avoid the regression? I'm just looking to debug with you, not defending the model. I've mostly used Opus 5 for code reviews & bugfixes.
Yeah fine. I mean my plan wasn't to difficult. For example this morning I started with Opus 5 to tackle a problem. During planning at some point Opus 5 detected _8_ regressions in it's own planning, after I directed it towards those potential regressions. So, in this very moment now, Fable 5 implements code already and the planning before with Fable, done with the same instructions, was flawless and quick. And I am sure, Opus 4.8 would be flawless either. Same harness, same claude.md, etc..