Simple demo for git bisect
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Simple Demo for Git Bisect

This git repository has only one purpose: It has a relatively long history with one harmful commit in there.

From this commit on, a script and a Java unit test start failing (that is, the script exits with status 1 and the unit test has an assertion error).

Just imagine, that all the commits between the tag base and the head of the master branchis the work of your day and you have not noticed these errors until, near the end of this day, you start the maven build and you see, that this is not working any more.

Without having git, you would now go deep into all of your changes you have done this day and would - maybe by just staring sense into the failures - try to find out what and (most importantly) when things turned out to go the wrong way.

But now you have git! You haven't heard about git bisect? Now it's definitely the right time to change this.

All you have to do is

  1. Go to the head of the master branch (if you aren't here already)

  2. Start git bisect, telling git that the current commit is bad:

    git bisect bad

    (Yes git, please start bisect for me)

  3. Checkout the last commit you know that was good:

    checkout base

    git bisect good

  4. Let git search for the foul commit, either

    • by executing commands and telling git whether the current commit is good or bad:

      git bisect good|bad

      Using this, you only would have to check some commits by hand until git tells you, that it has found the foul commit.

    • or by telling git to execute a command that tells it whether the commit is good or bad:

      git bisect run mvn test

      Now all you have to do is wait, until git tells you the result.

  5. When you're done, just stop the machinery:

    git bisect reset

Belief me, when you have seen this little magic, you will reconsider squashing commits.

Have fun!