There is a number of unit test frameworks for most of the languages, but I haven't come across a unit test for GNU make. It has conditionals, loops (the $(foreach ...) statement), and allows to write pretty sophisticated code. The examples might be things like BSD ports, GARNOME, and OpenCSW GAR.
There's also a debugger for GNU make. However, I've never come across a unit test framework for it. Is there anything like this in existence?
I would also see the build itself as the integration-test.
Usually problems with the build pop up early, especially if you have a working continous integration setup. In our case we have all possible build-paths run regularly run on our ci-servers (the software is constantly built and deployed).
As far as I remember if there was a problem with a build-script ci showed us a crash instantly, for instance because tar-ball could not be built, or application couldn't be started due to missing artifacts.
For above reasons, I think trying to unit-test the build-files itself involves too much effort, which could be spent better in setting up or extending continous integration.