$ git add --patch foo # add just first part to the index
$ git stash save --keep-index # save all other changes to the stash
$ edit/build/test first part
-$ git commit foo -m 'First part' # commit fully tested change
+$ git commit -m 'First part' # commit fully tested change
$ git stash pop # prepare to work on all other changes
# ... repeat above five steps until one commit remains ...
$ edit/build/test remaining parts