Oops, I see the code in the test is too optimized to cut&paste for a test.
To test against your database with a date value containing multilinks
you want to do something along the lines of
 
import sys
import os
from roundup import date, instance

dir     = os.getcwd ()
tracker = instance.open (dir)
db      = tracker.open ('admin')

print db.issue.filter (None, {}, ('+','id'), ('+', 'deadline'))

This groups by the date attribute "deadline" which you want to change if
your date attribute is named differently.