PRO TEST_ERROR
   ; Error handling code.
Catch, theError
IF theError NE 0 THEN BEGIN
   Catch, /Cancel
   Help, /Last_Message, Output=theErrorMessage
   FOR j=0,N_Elements(theErrorMessage)-1 DO BEGIN
      Print, theErrorMessage[j]
   ENDFOR
   RETURN
ENDIF
   ; The code that causes the error.
Print, xxx
END