To set up a simple systemd timer as a user on Debian 9.9, here are the following steps to make it work.
Systemd version :
As a user, both the .service unit and .timer unit must be located in $HOME/.config/systemd/user.
If this folder does not exist, create it :
mkdir -p $HOME/.config/systemd/user
If both the .service and .timer files are named as test, it must be enabled and started :
systemctl --user enable test
systemctl --user start test
The expected output should be found using journalctl :