It would be nice to have a condition which has a similar effect like the 'test -s' shell function.
Such a check would be useful for:
* working on read-only filesystems; when file is empty, another one is bind-mounted on it.
* dealing with errors during system initialization. E.g. when powering off the machine on ssh key generation an empty files might remain. Checking for pure existence of file won't be enough in this case.
Implemented in git.