anchor.diff:    (let ((add-100 (adder 100))
           (add-500 (adder 500)))
     "add-100 and add-500 now refer to different bindings to x"
  -   (assert-equal ___ (funcall add-100 3))
  -   (assert-equal ___ (funcall add-500 3))))
  +   (assert-equal 103 (funcall add-100 3))
  +   (assert-equal 503 (funcall add-500 3))))
   
   
   ;; ----
  
positive.code: 
  (define-test test-optional-parameters
      "Optional parameters are filled in with their default value."
     (assert-equal (func-with-opt-params :test-1 :test-2) ___)
     (assert-equal (func-with-opt-params :test-1) ___)
     (assert-equal (func-with-opt-params) ___))
  
  
  ;; ----
  
negative.code:     (setq f1 '+)
      (setq f2 '-)
      (setq f3 'max)
      (assert-equal 3 (funcall f1 1 2))
      (assert-equal -1 (funcall f2 1 2))
      (assert-equal 6 (funcall f1 1 2 3))
      (assert-equal 4 (funcall f3 1 2 3 4))))
  