git-remote-testgit man page
git-remote-testgit — Example remote-helper
git clone testgit::<source-repo> [<destination>]
This command is a simple remote-helper, that is used both as a testcase for the remote-helper functionality, and as an example to show remote-helper authors one possible implementation.
The best way to learn more is to read the comments and source code in git-remote-testgit.
Part of the git(1) suite