Tests/OutOfSource/OutOfSourceSubdir/testlib.h

#ifdef _WIN32
#  ifdef testlib_EXPORTS
#    define CM_TEST_LIB_EXPORT __declspec(dllexport)
#  else
#    define CM_TEST_LIB_EXPORT __declspec(dllimport)
#  endif
#else
#  define CM_TEST_LIB_EXPORT
#endif

CM_TEST_LIB_EXPORT float TestLib();