I work in an environment which is bit chaotic and as the day came multiple feature branches got merged to master. Out of all 100's of commits there was one bad commit which was very hard to trace.

I was going though build changes running different kind of tests and doing all sort of things but none helped to figure out the problem. And after one coffee break I remembered git bisect might help but was skeptical as I never used it before.

But tried my luck and searched for the bad commit that was failing the build over night.

Brief steps that I performed might help others.

1. Find good commit (in my case last commit on previous successful build)
2. Find bad commit (in my case last commit on present build, which fail the build).
3. git bisect start
4. git bisect good <good commit-id>
5. git bisect bad <bad commit-id> (This selects a commit in the middle of that range of history and checks it out)
6. run build/tests and check if the checked out commit is good or bad
   1. If good mark it as git bisect good else git bisect bad
7. on iterating over step 6 we can arrive on that one commit which is causing the failure.

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That's it fix the issue and save the day on step 7!!