CUnit
As the name says CUnit is an xUnit implementation for the C programming language.
In comparison to dynamic programming languages the test organization requires much more manual glue code. Because C has no introspection one has to register every test case manually. Likewise there is no support for utilities like mock object generation or annotations.
On the other hand unit tests can be very useful in C, for example when implementing data structures. Test cases may isolate null pointer dereferencing and one can use valgrind on them to detect memory leaks at the lowest level.