When you first install yaptest and try to use sudo you might get the following error:

$ sudo yaptest-nmap-udp.pl

ERROR: Environment variable YAPTEST_DBNAME is not set

 at /usr/local/lib/site_perl/yaptest.pm line 126

        yaptest::new('yaptest') called at /usr/local/bin/yaptest-hosts.pl line 8

        (in cleanup) Can't call method "disconnect" on an undefined value at /usr/local/lib/site_perl/yaptest.pm line 3247.

This is because sudo has (very sensibly) unset the environment variable YAPTEST_CONFIG_FILE which in turn prevents YAPTEST_DBNAME getting set.  The yaptest scripts no longer know which test they're supposed to be working on.

The solution is simple.  Add an entry like the following into /etc/sudoers: 

# Allow users in group users to export specific variables

Defaults:youruser      env_keep="DISPLAY YAPTEST_CONFIG_FILE"

This prevents sudo from unsetting the YAPTEST_CONFIG_FILE (and also DISPLAY because that can be a pain too).