Unit-Testing SICP

Recently while reading SICP I got an idea of ​​using unit-testing techniques to perform the exercises. This is a excellent way to practice both SICP and unit-testing. Because of using MIT Scheme, my choice fell on the library "test-manager" by Alexey Radul. It is really easy to use and contains all required features)

So, let's try to use it for the exercise 1.16.

Design a procedure that evolves an iterative exponentiation process that uses successive squaring and uses a logarithmic number of steps, as does fast-expt.

; code
(define (fast-expt b n)
 (define (iter a b n)
  (cond
   ((= n 1) (* a b))
   ((even? n) (iter a (* b b) (/ n 2)))
   (else (iter (* a b) b (- n 1)))))
 (iter 1 b n))

; tests
(load "test-manager/load.scm")
(define-each-test
  (assert= 1 (fast-expt 2 0))
  (assert= 2 (fast-expt 2 1))
  (assert= (expt 2 8) (fast-expt 2 8))
  (assert= (expt 2 6) (fast-expt 2 6)))

(run-registered-tests)

Run:

mit-scheme < ex1_16.scm

1 ]=> (run-registered-tests)

Oops! I completely forgot about condition when the exponent n is zero.
Fix it:

(define (fast-expt b n)
 (define (iter a b n)
  (cond
   ((= n 0) a)
   ((even? n) (iter a (* b b) (/ n 2)))
   (else (iter (* a b) b (- n 1)))))
 (iter 1 b n))

Run it again:

1 ]=> (run-registered-tests)....

4 tests, 0 failures, 0 errors.

That's it!