Hacking on Déjà Dup
Getting Source Directly
You can directly get the trunk and build from there:
git clone https://gitlab.gnome.org/World/deja-dup.git cd deja-dup make
Things to Do
There is a list of tasks to take on.
Run ./tests/shell-local to get a shell that points to your built executables and uses a temporary gsettings location so you don't mess with your user's settings.
Once in that shell, you can run commands like deja-dup --backup or deja-dup to test your changes.