Make sure you know about exit code 125 to your test script. You can use it in those terrible cases where the test can't tell, one way or another, whether the failure you seek happened, for example when there is an unrelated build problem.

I wrote a short post on this:

https://speechcode.com/blog/git-bisect

Related advice, in any repo where merge commits represent integration points (such as PRs must build and pass CI tests before merging and PRs produce merge commits) you can use `git bisect --first-parent` to just bisect your high-level merge commits which you know should build. Often knowing "which PR introduced this bug" is as handy as knowing which commit did it. But once you find the PR merge commit you can also run a quick second bisect on just that branch to find the lower level commit.