Git bisect is my friend

Recently when I did a merge on one of my projects, large number of commits got merged. I found that my tests were broken. It became a tedious task for me to find out which commit exactly broke the tests among those which got merged.

Into the scene: Vagmi Mudumbai(CTO of Dharana)

“Git-bisect should be your friend.”

I have never tried git-bisect, I thought I will give a try. Tasting the sweet of awesomeness. Git-bisect takes in a good commit(a commit where your tests passed) and a bad commit(a commit where your tests failed, mostly HEAD). Git-bisect allows you to run tests in between your commits and will ask you to mark them good or bad based on which you can narrow down your search. Aaahh, now I see you remember binary search!!!! Yeah, thats exactly what git-bisect does and here is how you do it.

$ git bisect start
$ git bisect good 9ef9b9a64a
$ git bisect bad b5e38ab73b
> Bisecting: 60 revisions left to test after this (roughly 6 steps)

What happens now is little interesting, git will put you on to a ‘bisect’ branch that is somewhere in between your good and bad commit. Now all you have do is to run the tests and find out if it still fails or not. Lets assume your tests failed, so you have to tell git that this commit is bad.(If it passes you have to say its good.)

$ git bisect bad
> Bisecting: 29 revisions left to test after this (roughly 5 steps)

You have now got a different commit to test, and you have only 29 commits left to check. The idea is to make you not to step through every single commit to find that bad commit. Now run the tests again and tell git if this commit is good or bad. When you continue doing this you will eventually find out the commit which broke the tests, and wait git will also estimate how many steps are roughly required to find out that bad commit. Awesome!!!!!

> 6247d67284798e40182034500305b282dccf4a6a is the first bad commit

Tadaaaaa, now you can go and fight with that guy who broke all your tests. Finally if you see that your boss was the one who broke your tests, and you want to go back to current state and fix it all by yourself, you have to say,

$ git bisect reset

Happy fighting, happy testing.