The program qmail-dnstest is actually dnsclient. It do all in the same way as qmail and print the same exit status (DNS_SOFT, DNS_HARD, DNS_MEM) like qmail. It is designed to check qmail functions before linking with qmail.a. If you need dns_txt() link only with qmail_txt.a.
HTML documentation is not ready.
See included file README.qmail in
qmail+djbdns.tar.gz.
If someone write documentation - it's welcome!
My english is pure and I dislike writing docs.