Unit Testing with RackUnit | Schema Programming Part 21

Racket takes testing seriously. The standard library rackunit is baked into the language ethos, making it easy to write tests directly alongside your code.

Basic Checks

The simplest test is check-equal?.

#lang racket
(require rackunit)

(define (add x y) (+ x y))

(check-equal? (add 1 1) 2 "Simple math should work")
(check-equal? (add -1 1) 0 "Negative numbers work")

If these pass, nothing happens (silence is golden). If they fail, you get a detailed error report.

Test Cases and Suites

For larger projects, group your checks.

(require rackunit/text-ui)

(define-test-suite math-suite
  (test-case
   "Addition tests"
   (check-equal? (+ 2 2) 4)
   (check-equal? (+ 0 0) 0))
  
  (test-case
   "Multiplication tests"
   (check-equal? (* 2 3) 6)))

(run-tests math-suite)

Testing Exceptions

You can verify that your code errors when it's supposed to!

(check-exn exn:fail? 
           (lambda () (/ 1 0)))

Organizing Tests in Modules

A common pattern is to put tests in a submodule so they don't run when you import the library, only when you run the file directly or use raco test.

(module+ test
  (require rackunit)
  (check-equal? (my-func 10) 100))

Run them with:

raco test my-file.rkt

Summary

RackUnit isn't an addon; it's a core part of the Racket experience. Using module+ test allows you to keep tests close to the code without bloating your production builds.