Sometimes I’ll patch a production bug in my production branch and then I will forget to merge that commit into the development branch. This is how I can check for that:

$ git checkout production_branch
$ git cherry dev_branch

This will spit out a list of commits that are in production_branch but not in dev_branch. It will not return any commits made to dev_branch but not in production_branch. It is not the same as a diff of the two branches either.