I was working on homework that challenged us to create tests to build a rails app from the ground up. We had to learn how to create new database entries, save them, and edit them. I finished the homework on a master branch and decided I wanted to do it again for practice. So I created a topic branch off of an early commit (e3f8704) to do the work from scratch.
$ git checkout -b homework e3f8704
Later I realized I made a mistake and needed to use interactive rebase to fix a commit message on the topic branch. To do so, I just passed in the commit I used to branch as an option. This tells Git that you want to rebase from that commit.
$ git checkout homework $ git rebase -i e3f8704