This applet has no unittests (yet).

In order to test changes you need to kill update-notifier from your
running session (there can only be one) and start it from your local
build dir. Make sure you build with --prefix=/usr (or some other
location where your ui files are). Then you can do the
following:

Test updates:
Install a package from a previous version and check if update-notifier
detects that and shows a update icon. Run apt-get update and check if
it detects that a package manager is running.

Test hooks:
Copy a example hook file into /usr/lib/update-notifier/user.d/ (or
touch it) and touch /var/lib/update-notifier/dpkg-run-stamp to trigger
it reading the hooks.  Modify ~/.update-notifier/hooks_seen to
simulate certain conditions. Add identical files to "user.d" to test
the duplicates detection.

Test reboot notification:
Run /usr/share/update-notifier/notify-reboot-required and then do
touch /var/lib/update-notifier/dpkg-run-stamp.

Test cdrom detection:
Put a ubuntu CD into the driver and verify that its detected.

Test auto-launch:
The "faketime" package is useful for testing the auto-launch
funtionatliy
$ NO_FAKE_STAT=1 faketime '10 days' update-notifier --debug-updates
# aftwards the launch time in u-m needs to be reset
$ gsettings reset com.ubuntu.update-manager launch-time