anchor.diff:    (is-true (let ((rod (rod "aha")))
                (eql rod (nrod-downcase rod)))))
   
  -(test nrod-downcase.4
  +(test nrod-downcase.error.1
     (signals type-error
       (nrod-downcase 5)))
   
positive.code:   (is-false (let ((rod (rod "AHA")))
                (eql rod (rod-upcase rod)))))
  
  (test rod-upcase.4
    (signals type-error
      (rod-upcase 5)))
  
negative.code:   (is-false (let ((rod (rod "aha")))
                (eql rod (rod-downcase rod)))))
  
  (test rod-downcase.error.1
    (signals type-error
      (rod-downcase 5)))
  