Allows a principal to test whether an attribute of a name has
  a particular value without being able to actually see any of
  the values (that is, without having read access to the name).

  The main benefit of test access is that it gives application pro-
  grammers a more efficient way to verify an attribute value.
  Rather than reading the entire set of values, an application
  can test for the presence of a particular value.  DECdns itself
  uses this function to test for group membership during access
  checking.  You should grant at least test access to all users
  of client applications that use the test function on their own
  objects.