`git bisect (start`

git bisect (start | good | bad | skip | run | log | reset)

Risk: Careful

What it does

Finds the commit that broke something by halving the history.

When it worked before and you don't know which commit broke it.

$ git bisect start HEAD HEAD~9

Bad is HEAD, good is nine commits back. Git checks out the middle.

$ git bisect good

The commit you are testing works.

$ git bisect bad

The commit you are testing is broken.

$ git bisect run sh test.sh

Let a test script judge every step for you.

$ git bisect reset

Finish and go back to your branch.