There's a slowly growing test suite in tests/.  To build install libtap
from http://www.shlomifish.org/open-source/projects/libtap/ *, then build
the "check" target.  e.g. "make check".  This builds and runs any tests.

*Unpack the tarball with "gunzip tap-1.03.tar.gz && tar xf tap-1.03.tar"
instead of the usual tar command.