anchor.diff:  (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))
  +      (assert-equal 0 (how-many-value-queries x))
         ; check that the default value is zero.
  -      (assert-equal ___ (get-value x))
  +      (assert-equal 0 (get-value x))
         ; now that we've looked at it, there is a single access.
  -      (assert-equal ___ (how-many-value-queries x))
  +      (assert-equal 1 (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))))
  +      (assert-equal 3 (how-many-value-queries x))))
   
   
   ; countdowner has a value which goes down every time you look at it
  
positive.code: ;; to satisfy the test-countdowner tests.
  ;; you may be interested in the 'decf function.
  (defmethod get-value ((object countdowner))
    :WRITE-ME)
  
  
  (define-test test-countdowner
  
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
  