HUnit is a unit testing framework for Haskell, inspired by the JUnit tool for Java. This guide describes how to use HUnit, assuming you are familiar with Haskell, though not necessarily with JUnit.

In the Haskell module where your tests will reside, import module Test.HUnit:

   import Test.HUnit

Define test cases as appropriate:

   test1 = TestCase (assertEqual "for (foo 3)," (1,2) (foo 3))
   test2 = TestCase (do (x,y) <- partA 3
                        assertEqual "for the first result of partA," 5 x
                        b <- partB y
                        assertBool ("(partB " ++ show y ++ ") failed") b)

Name the test cases and group them together:

   tests = TestList [TestLabel "test1" test1, TestLabel "test2" test2]

Run the tests as a group. At a Haskell interpreter prompt, apply the function runTestTT to the collected tests. (The TT suggests Text orientation with output to the Terminal.)

   > runTestTT tests
   Cases: 2  Tried: 2  Errors: 0  Failures: 0
   >

If the tests are proving their worth, you might see:

   > runTestTT tests
   ### Failure in: 0:test1
   for (foo 3),
   expected: (1,2)
    but got: (1,3)
   Cases: 2  Tried: 2  Errors: 0  Failures: 1
   >

You can specify tests even more succinctly using operators and overloaded functions that HUnit provides:

   tests = test [ "test1" ~: "(foo 3)" ~: (1,2) ~=? (foo 3),
                  "test2" ~: do (x, y) <- partA 3
                                assertEqual "for the first result of partA," 5 x
                                partB y @? "(partB " ++ show y ++ ") failed" ]

Assuming the same test failures as before, you would see:

   > runTestTT tests
   ### Failure in: 0:test1:(foo 3)
   expected: (1,2)
    but got: (1,3)
   Cases: 2  Tried: 2  Errors: 0  Failures: 1
   >