anchor.diff:    1)
   
   (define-test test-return-from-function-early
  -   (assert-equal (sign-of -5.5) ___)
  -   (assert-equal (sign-of 0) ___)
  -   (assert-equal (sign-of ___) 1))
  +   (assert-equal (sign-of -5.5) -1)
  +   (assert-equal (sign-of 0) 0)
  +   (assert-equal (sign-of 5) 1))
   
   
   ;; ----
  
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) '(:test-1 :test-2))
     (assert-equal (func-with-opt-params :test-1) '(test-1 3))
     (assert-equal (func-with-opt-params) '(2 3)))
  
  
  
negative.code: 
  (define-test test-key-params-can-have-defaults
      "key parameters can have defaults also"
     (assert-equal (func-key-params-can-have-defaults) '(3 nil 4 nil))
     (assert-equal (func-key-params-can-have-defaults :a 3 :b 4) '(3 t 4 t))
     (assert-equal (func-key-params-can-have-defaults :a 11 :b 22) '(11 t 22 t))
     (assert-equal (func-key-params-can-have-defaults :b 22) '(3 nil 22 t))
     ; order is not important
     (assert-equal (func-key-params-can-have-defaults :b 22 :a 0) '(0 t 22 t)))
  
  
  ;; ----
  