@b0rk If you think you may have messed up (and your history is linear) because you keep getting "bad" commits: do git bisect log
and retest the most recent "good" commit. And the reverse if you keep getting "good" commits.
I also like to do this as a final check after the bisect completes.
If you did mess up, you can use the output from git bisect log
to restart your bisect without having to redo any tests.
Probably also applies when using --first-parent but I'm not familiar with it.