1 Quick Start Guide for RackUnit 🔗

Suppose we have code contained in file.rkt, which implements buggy versions of + and * called my-+ and my-*:

#lang racket/base
 
(define (my-+ a b)
  (if (zero? a)
      b
      (my-+ (sub1 a) (add1 b))))
 
(define (my-* a b)
  (if (zero? a)
      b
      (my-* (sub1 a) (my-+ b b))))
 
(provide my-+
         my-*)

We want to test this code with RackUnit. We start by creating a file called file-test.rkt to contain our tests. At the top of file-test.rkt we import RackUnit and file.rkt:

#lang racket/base
 
(require rackunit
         "file.rkt")

Now we add some tests to check our library:

(check-equal? (my-+ 1 1) 2 "Simple addition")
(check-equal? (my-* 1 2) 2 "Simple multiplication")

This is all it takes to define tests in RackUnit. Now evaluate this file and see if the library is correct. Here’s the result I get:

--------------------

FAILURE

name:       check-equal?

location:   (file-test.rkt 7 0 117 27)

expression: (check-equal? (my-* 1 2) 2)

params:     (4 2)

message:    "Simple multiplication"

actual:     4

expected:   2

 

--------------------

The first test passed and so prints nothing. The second test failed, as shown by the message.

Requiring RackUnit and writing checks is all you need to get started testing, but let’s take a little bit more time to look at some features beyond the essentials.

Let’s say we want to check that a number of properties hold. How do we do this? So far we’ve only seen checks of a single expression. In RackUnit a check is always a single expression, but we can group checks into units called test cases. Here’s a simple test case written using the test-begin form:

(test-begin
 (let ([lst (list 2 4 6 9)])
   (check = (length lst) 4)
   (for-each
    (lambda (elt)
      (check-pred even? elt))
    lst)))

Evalute this and you should see an error message like:

--------------------

A test

... has a FAILURE

name:       check-pred

location:   (#<path:/Users/noel/programming/schematics/rackunit/branches/v3/doc/file-test.rkt> 14 6 252 22)

expression: (check-pred even? elt)

params:     (#<procedure:even?> 9)

--------------------

This tells us that the expression (check-pred even? elt) failed. The arguments of this check were even? and 9, and as 9 is not even the check failed. A test case fails as soon as any check within it fails, and no further checks are evaluated once this takes place.

Naming our test cases is useful as it helps remind us what we’re testing. We can give a test case a name with the test-case form:

(test-case
 "List has length 4 and all elements even"
 (let ([lst (list 2 4 6 9)])
   (check = (length lst) 4)
   (for-each
    (lambda (elt)
      (check-pred even? elt))
    lst)))

Now if we want to structure our tests a bit more we can group them into a test suite:

(define file-tests
  (test-suite
   "Tests for file.rkt"
 
   (check-equal? (my-+ 1 1) 2 "Simple addition")
 
   (check-equal? (my-* 1 2) 2 "Simple multiplication")
 
   (test-case
    "List has length 4 and all elements even"
    (let ([lst (list 2 4 6 9)])
      (check = (length lst) 4)
      (for-each
        (lambda (elt)
          (check-pred even? elt))
      lst)))))

Evaluate the module now and you’ll see the tests no longer run. This is because test suites delay execution of their tests, allowing you to choose how you run your tests. You might, for example, print the results to the screen or log them to a file.

Let’s run our tests, using RackUnit’s simple textual user interface (there are fancier interfaces available but this will do for our example). In file-test.rkt add the following lines:

(require rackunit/text-ui)
 
(run-tests file-tests)

Now evaluate the file and you should see similar output again.

These are the basics of RackUnit. Refer to the documentation below for more advanced topics, such as defining your own checks. Have fun!