I think it works ok if you make a new branch from a known good commit, add the test, then rebase the new changes on top. You could do that with
git checkout -b testing git rebase -i HEAD~50 (or whatever) move test commit to bottom, then save.
git checkout -b testing git rebase -i HEAD~50 (or whatever) move test commit to bottom, then save.
The best part is I should be able to resolve any conflicts before I start bisecting.
Where's the "accept as the right answer" check mark? :)