In the Debian Edu / Skolelinux project, we include a post-installation test suite, which check that services are running, working, and return the expected results. It runs automatically just after the first boot on test installations (using test ISOs), but not on production installations (using non-test ISOs). It test that the LDAP service is operating, Kerberos is responding, DNS is replying, file systems are online resizable, etc, etc. And it check that the PXE service is configured, which is the topic of this post.
The last week I've fixed the DVD and USB stick ISOs for our Debian Edu Wheezy release. These ISOs are supposed to be able to install a complete system without any Internet connection, but for that to happen all the needed packages need to be on them. Thanks to our test suite, I discovered that we had forgotten to adjust our PXE setup to cope with the new names and paths used by the netboot d-i packages. When Internet connectivity was available, the installer fall back to using wget to fetch d-i boot images, but when offline it require working packages to get it working. And the packages changed name from debian-installer-6.0-netboot-$arch to debian-installer-7.0-netboot-$arch, we no longer pulled in the packages during installation. Without our test suite, I suspect we would never have discovered this before release. Now it is fixed right after we got the ISOs operational.
Another by-product of the test suite is that we can ask system administrators with problems getting Debian Edu to work, to run the test suite using /usr/sbin/debian-edu-test-install and see if any errors are detected. This usually pinpoint the subsystem causing the problem.