If building with hardened build flags, such as -fPIC (which the Fedora package builders do), the -fPIC is not passed to the C compiler by the Vala build rule. This leads to a compile failure when building the tests in the Fedora package. The build rule should probably be changed to use the Automake rules (although those are not that great), but it is also sufficient to pass -fPIC straight to the Vala compiler.