Accept None for the missing inputs, output, exclude and keep values and replace them with their defaults in __init__, and annotate the SSH client, which mypy typed as None and so skipped checking the remote code.
Run real rsync into a temp dir to test hard links, keep, remove-before-backup, stray files in the backup dir and the old folder name format, and use a fake Popen to test how rsync return codes are handled.
Fuxino
