The recipe you used for testing is:

:0:
* ^Subject:.*test
IN.testing


The meaning of this recipe is:

Notation            Meaning
========            =======
:0                  Begin a recipe
  :                 Use a lock file
*                   Begin a condition 
  ^                 Match the beginning of a line followed by....
   Subject:         ``Subject:'' followed by....
           .        any character (.) followed by....
            *       0 or more of preceding character (any character in this 
                       case) followed by....
              test  ``test''
IN.testing          If successful match, put in folder $MAILDIR/IN.testing