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: (define-test test-inheritance
      (let ((circle-1 (make-instance 'circle))
            (shape-1 (make-instance 'shape)))
        (assert-equal ____ (type-of shape-1))
        (assert-equal ____ (type-of circle-1))
        (true-or-false? ____ (typep circle-1 'circle))
        (true-or-false? ____ (typep circle-1 'shape))
        (set-kind :circle circle-1)
        (set-pos '(3 4) circle-1)
        (set-radius 5 circle-1)
        (assert-equal ____ (get-pos circle-1))
        (assert-equal ____ (get-radius circle-1))))
  
  ;; Classes may also inherit from more than one base class.
  ;; This is known as multiple inheritance.
  
negative.code:           (my-circle (make-instance 'circle))
            (my-color (make-instance 'color)))
        (get-kind my-shape)
        (assert-equal :shape *last-kind-accessor*)
        (get-kind my-circle)
        (assert-equal :circle *last-kind-accessor*)
        (get-kind my-color)
        (assert-equal :color *last-kind-accessor*)
        (get-kind my-colored-circle)
        (assert-equal :color *last-kind-accessor*)
        (get-kind my-circled-color)
        (assert-equal :circle *last-kind-accessor*)))
  
  
  ;; Todo: consider adding :before and :after method control instructions.
  