;unit-testing.scm
(define-syntax test
  (syntax-rules ()
    ((_expression expected-result)
     (list (quote expression) expected-result))))
(define (run-test the-test)
  (let ((expression (car the-test)))
    (write expression)
    (let* ((result (eval expression (interaction-environment)))
           (status (equal? (cadr the-test) result)))
      (if status
          (display "ok")
          (display "fail"))
      (newline)
      (if (not status)
          (begin
            (display " Expected: ")
            (write (cadr the-test))
            (newline)
            (display "Returned: ")
            (write result)
            (newline)))
      status)))
(define (run-tests the-tests)
  (define (and-fold x xs)
    (if (null? xs)
        x
        (and-fold (and x (car xs)) (cdr xs))))
  (and-fold #t (map run-test the-tests)))
(define(signum x)
  (cond
    (( < x 0) -1)
    ((= x 0) 1)
    (else 1)))
(define the-tests
  (list (test (signum -2) -1)
        (test (signum 0) 0)
        (test (signum 2) 1)))
(run-tests the-tests)