anchor.diff:  (define (reset-testing )
     (set! number-of-passes 0)
     (set! number-of-failures 0)
  +  (set! number-of-errors 0)
     (set! failure-messages '())
  +  (set! error-messages '())
     (set! verbose-tests nil))
   
   (define (log-pass msg)
  
positive.code:               (for-each (lambda (it-clause)
                            ,@setup
                            (eval it-clause))
                     ',body))))
  
  (defmacro (it label . body)
    (if (not (or (symbol? label) (string? label)))
  
negative.code:                  (log-failure msg "expected an error, but there wasn't")))))
  
  (define (dump-summary duration)
    (format #t "~%Ran ~A tests in ~A seconds~%"
            (+ number-of-passes number-of-failures number-of-errors)
            (/ duration 1000.0))
    (format #t "~A passes, ~A failures, ~A errors~%"
  