For example, if you build and run the test like this:
./opal_path_nfs . Makefile ~
It'll report if ., Makefile, and ~ are on network filesystems (i.e., the result of sending each of ".", "Makefile", and "your_home_dir" to opal_path_nfs()).
I already have NFS mounts on my Solaris systems and was able to mount something on my OpenBSD and NetBSD systems, too. So, I'll try to remember to use the command-line test on those systems. My FreeBSD systems are VMs without any (practical) way to NFS mount anything, but I can at least check for false positives.