Find out if library is in path

Assuming I want to test if a library is installed and usable by a program. I can use ldconfig -p | grep mylib to find out if it's installed on the system. but what if the library is only known via setting LD_LIBRARY_PATH? In that case, the program may be able to find the library, but ldconfig won't. How can I check if the library is in the *combined* linker path? I'll add that I'm looking for a solution that will work even if I don't actually have the program at hand (e.g. the program isn't compiled yet), I just want to know that a certain library exists in ld's paths.