First a positive feedback: good and instructive documentation, good start for a new project!
In chapter "Installing Cgreen" there's the sentence: "A test can be any function with a void (void) signature."
This is not true, for instance, if you define a test "void testFoo(void)" and add it with add_test, the code will compile (with gcc 3.4.4) with a warning: "passing arg 3 of `_add_test' from incompatible pointer type". This happens because void testFoo(void) and void testFoo() (as in your examples) are different things.
Obsolete.