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:           (my-circle (make-instance 'circle))
            (my-color (make-instance 'color)))
        (get-kind my-shape)
        (assert-equal ____ *last-kind-accessor*)
        (get-kind my-circle)
        (assert-equal ____ *last-kind-accessor*)
        (get-kind my-color)
        (assert-equal ____ *last-kind-accessor*)
        (get-kind my-colored-circle)
        (assert-equal ____ *last-kind-accessor*)
        (get-kind my-circled-color)
        (assert-equal ____ *last-kind-accessor*)))
  
  
  ;; Todo: consider adding :before and :after method control instructions.
  
negative.code: (define-test test-clos-getters-and-setters
      (let ((ship-1 (make-instance 'spaceship)))
        (set-color :orange ship-1)
        (assert-equal :orange (get-color ship-1))
        (set-speed 1000 ship-1)
        (assert-equal 1000 (get-speed ship-1))))
  
  ;; CLOS also provides functionality to create accessors
  ;; to object data.
  