Testing of wipe involves examining each pass, to ensure completeness
and correctness. First add '#define PAUSE' to debug.h and
compile. Next, run wipe -vKD -x1 <file>. After each pass, use hexdump,
ghex, or khexdit to view the pattern. Look for breaks in the sequence,
for multi-byte passes. For single byte passes, just run hexdump; it'll
make it obvious if the whole file isn't filled with the same byte. The
most difficult to verify is the random pass. There are basically three
ways to check entropy. The first way is to run hexdump, pick some
sequences two to four bytes long, and hexdump | grep them, to see how
many times they appear. The longer the sequence, the less likely it is
to appear more than once. This is obviously not the best method. The
second method is to run a compression algorithm on the data. The
greater the entropy, the less effective the compression (in fact,
compression is often used to increase hash input randomness). I tested
both gzip and bzip2, using -9, and the output of both was larger than
the original file.

The third method, which I have not done, is to make a histogram of
PRNG output, and make sure it has decent distribution. Distribution
isn't too much of an issue, since this isn't a monte carlo application
and it doesn't require cryptographically strong entropy. However,
there shouldn't be any big spikes.