The tdd-util package

[Tags:bsd3, library]

tdd-util is a small test framework for TDD (cf. that integrates three testing libraries, whose modules are all exported under Test.Util.Framework, while providing utilities based on each of these, exported under Test.Util, by wrapping the library test-framework.

Getting Started

To get started, an example that uses this library is this library's test suite itself and can be found at Each module under src corresponds with a module under testsrc/Test that contains the tests for that module. (For example, this library currently exports two modules in src/Test/Util.hs and src/Test/Util/Framework.hs; their tests are located, respectively, in testsrc/Test/Test/Util.hs and testsrc/Test/Test/Util/Framework.hs; and a module in src/Data/Trie.hs would correspond with a test module in testsrc/Test/Trie.hs). This structure can be conveniently cargo culted from this library, but these conventions are not enforced.

Test Modules

Conventially, each module in src/X.hs corresponds with a module that contains tests for that module located at testsrc/Test/X.hs. None of these Test modules depend on each other by importing them. For a concrete example of such a test module, see

Each test module exports a list of test-framework's TTests (an alias to disambiguate between Test types from different libraries) named tests.

This list of tests can either be run individually by importing the test module, and then running defaultMain tests; or be grouped together in the test-suite's Tests module (see below).

In the tests themselves, very briefly, testGroup "Brief description of test" […] can be used to construct a single test-framework test (TTest) from a group of other tests, testProperty name prop_foo can be used to construct a TTest from a QuickCheck property, and testCase name $ do … can be used to construct a test from HUnit. See test-framework's documentation for more information about constructing QuickCheck and HUnit properties.

Here is a segment of code from

module Test.Test.Util
( tests
) where

import Control.Applicative
import Text.Printf

import Test.Util
import Test.Util.Framework
tests :: [TTest]
tests =
[ testGroup "Throwing and catching exceptions - isExceptionThrown" $
[ testCase "throwing an exception" $ do
thrown <- isExceptionThrown $ do
throwIO $ AssertionFailed "assertion failed"
when (either (e -> flip const (e :: AssertionFailed) $ False) (const True) $ thrown) $ do
assertString "exception NOT thrown"
, testCase "not throwing an exception" $ do
thrown <- isExceptionThrown $ do
return ()
when (either (e -> flip const (e :: AssertionFailed) $ True) (const False) $ thrown) $ do
assertString "exception thrown"
, testGroup "Throwing and catching exceptions - assert*Thrown" $


Each test module is conventionally grouped into a single test module, at testsrc/Tests.hs (e.g. see, that exports a list of TTests named tests. Interactively, this test module can be loaded in ghci, and the tests can be run as before, with defaultMain tests.

These tests can also be specified in the project's cabal file, by invoking defaultMain on tests in an external Main.hs file under testsrc (e.g. see Running this Main.hs will result in the test suite being run, so a test-suite section can be added to the cabal file as it is in

When a test suite is specified, cabal will recognized it and, when configured to do so, will run it when installing your package, resulting in output that may look like this when it succeeds.

Running 1 test suites...
Test suite tdd-util-tests: RUNNING...
Test suite tdd-util-tests: PASS
Test suite logged to: dist/test/tdd-util-
1 of 1 test suites (1 of 1 test cases) passed.

This package's Tests.hs:

module Tests
( tests
) where

import Test.Util.Framework

import qualified Test.Test.Util
import qualified Test.Test.Util.Framework

tests :: [TTest]
tests =
[ testGroup "Test.Test.Util.tests" $ Test.Test.Util.tests
, testGroup "Test.Test.Util.Framework.tests" $ Test.Test.Util.Framework.tests

Main.hs Example

Main.hs conventially defines a simple program that invokes defaultMain tests from the test group that encapsulates the entire test suite in Tests.hs. Here is this package's Main.hs file:

module Main where

import Test.Util.Framework

import Tests

main :: IO ()
main = do
defaultMain tests

Cabal Configuration

Your package's cabal configuration can be updated to point to testsrc/Main.hs/; here is a segment in this package's Cabal file that contains part of the specification for the package's test suite:

test-suite tdd-util-tests
type: exitcode-stdio-1.0
default-language: Haskell2010
hs-source-dirs: testsrc, src
ghc-options: -Wall -threaded
main-is: Main.hs

Note that tdd-util is the only TDD library one needs to depend on, if one only uses QuickCheck, HUnit, and test-framework via Test.Util.Framework; this omission is strictly optional, of course.

Test Running Example

Here is the output of importing Test.Test.Util inside the testsrc directory and then running tests on my system (note this is not the result of running the entire test suite; to do that, either run Main.hs or run, with defaultMain, the tests exported from Tests.hs rather than Test.Test.Util), without the coloured formatting:

% ghci Test.Test.Util
GHCi, version 7.6.1:  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Test.Test.Util   ( Test/Test/Util.hs, interpreted )
Ok, modules loaded: Test.Test.Util.

*Test.Test.Util> defaultMain tests
Loading package pretty- ... linking ... done.
Loading package tdd-util- ... linking ... done.
Throwing and catching exceptions - isExceptionThrown:
throwing an exception: [OK]
not throwing an exception: [OK]
Throwing and catching exceptions - assert*Thrown:
throwing an exception: [OK]
not throwing an exception: [OK]
isExceptionThrown -> assert*Thrown:
Applying appropriate assert*Thrown given result of isExceptionThrown: [OK, passed 100 tests]
Timed tests:
timeMicroseconds is accurate for random sleep times within 10ms: [OK, passed 100 tests]
timeMicroseconds is accurate for random delay times by timeout within 10ms: [OK, passed 100 tests]
timeoutMicroseconds behaves like timeout and throws exceptions appropriately:
timeoutMicroseconds overflow: [OK]
timeoutMicroseconds non-overflow: [OK]
waiting for a random amount of time from 0ms - 600ms; measured time difference is less than 10ms: [OK, passed 100 tests]
timeoutMicroseconds -> assertMicroseconds (assert*Thrown): [OK, passed 100 tests]
timeoutProcessMicroseconds behaves like timeoutMicroseconds and throws exceptions appropriately:
timeoutProcessMicroseconds overflow: [OK]
timeoutProcessMicroseconds non-overflow: [OK]
random sleep times and timeouts; return value is appropriate (NB: requires -threaded to work properly): [OK, passed 100 tests]
timeoutProcessMicroseconds -> assertProcessMicroseconds (assert*Thrown): [OK, passed 100 tests]

Properties  Test Cases  Total
Passed  7           8           15
Failed  0           0           0
Total   7           8           15


Dependencies base (>=4 && <6), HUnit, lens, MonadCatchIO-transformers, parallel-io, process, QuickCheck (==2.*), random, tagged, test-framework, test-framework-hunit, test-framework-quickcheck2, time, transformers [details]
License BSD3
Copyright Copyright (c) 2012 Byron James Johnson
Author Byron James Johnson
Maintainer Byron James Johnson <>
Stability Unknown
Category Testing
Source repository head: git clone git://
Uploaded Tue Oct 22 03:56:15 UTC 2013 by ByronJohnson
Distributions NixOS:
Downloads 1082 total (15 in the last 30 days)
0 []
Status Docs available [build log]
Successful builds reported [all 1 reports]




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