anchor.diff:  ;; to satisfy the test-countdowner tests.
   ;; you may be interested in the 'decf function.
   (defmethod get-value ((object countdowner))
  -  :WRITE-ME)
  +  (if (> (slot-value object 'value) 1)
  +      (decf (slot-value object 'value))
  +      "bang")
  +  )
   
   
   (define-test test-countdowner
  
positive.code: (define-test test-access-counter
      (let ((x (make-instance 'value-with-access-counter)))
        ; check that no one has ever looked at the x value yet.
        (assert-equal ____ (how-many-value-queries x))
        ; check that the default value is zero.
        (assert-equal ___ (get-value x))
        ; now that we've looked at it, there is a single access.
        (assert-equal ___ (how-many-value-queries x))
        ; check that we can set and read the value
        (set-value 33 x)
        (assert-equal 33 (get-value x))
        (assert-equal ___ (how-many-value-queries x))))
  
  
  ; countdowner has a value which goes down every time you look at it
  
negative.code:       (setf (slot-value car-1 'speed) 220)
        (setf (slot-value car-2 'color) :blue)
        (setf (slot-value car-2 'speed) 240)
        (assert-equal :red (slot-value car-1 'color))
        (assert-equal 240 (slot-value car-2 'speed))))
  
  ;; CLOS provides functionality for creating getters / setters
  ;; for defined objects
  