MIT licensed by Luke Murphy
Maintained by John Ky
This version can be pinned in stack with:tasty-discover-5.0.0@sha256:2799d2aa77c124e3f842abed9db7e8df260fe3d786549c293a322889c05484a8,6074
Used by 1 package in nightly-2024-04-18(full list with versions):

CircleCI tasty-discover-nightly tasty-discover-lts Hackage Status GitHub license


Haskell auto-magic test discovery and runner for the tasty test framework.

Prefix your test case names and tasty-discover will discover, collect and run them. All popular Haskell test libraries are covered. Configure once then just write your tests. Remember to add your test modules to your Cabal/Hpack files. Tasty ingredients are included along with various configuration options for different use cases.

See below for full documentation and examples.

Getting Started

There are 4 simple steps:

  1. Create a test driver file in the test directory
  2. Mark the driver file as the main-is in the test suite
  3. Mark tests with the correct prefixes
  4. Customise test discovery as needed

Check out the example project to get moving quickly.

Create Test Driver File

You can name this file anything you want but it must contain the correct preprocessor definition for tasty-discover to run and to detect the configuration. It should be at the top level of the test directory.

For example (in test/Driver.hs):

{-# OPTIONS_GHC -F -pgmF tasty-discover #-}

Configure Cabal or Hpack Test Suite

In order for Cabal/Stack to know where the tests are, you’ll need to configure the main-is option of your test-suite to point to the driver file. In the following example, the test driver file is called Driver.hs:

test-suite test
  main-is: Driver.hs
  hs-source-dirs: test
  build-depends: base

If you use hpack, that might look like:

    main: "Driver.hs"
    source-dirs: "test"
    - "base"

To ensure that tasty-discover is available even without installation, add this to the test suite in your cabal file:


See hpack documentation for stack equivalent.

Write Tests

Create test modules and prefix the test function name with an identifier that corresponds to the testing library you wish to run the test with:

Here is an example test module with a bunch of different tests:

{-# LANGUAGE ScopedTypeVariables #-}

module ExampleTest where

import Data.List
import Test.Tasty
import Test.Tasty.Discover
import Test.Tasty.HUnit
import Test.Tasty.Hspec
import Test.Tasty.QuickCheck

-- HUnit test case
unit_listCompare :: IO ()
unit_listCompare = [1, 2, 3] `compare` [1,2] @?= GT

-- QuickCheck property
prop_additionCommutative :: Int -> Int -> Bool
prop_additionCommutative a b = a + b == b + a

-- SmallCheck property
scprop_sortReverse :: [Int] -> Bool
scprop_sortReverse list = sort list == sort (reverse list)

-- Hspec specification
spec_prelude :: Spec
spec_prelude = describe "Prelude.head" $ do
  it "returns the first element of a list" $ do
    head [23 ..] `shouldBe` (23 :: Int)

-- Custom test
-- Write a test for anything with a Tasty instance
-- In order to use this feature, you must add tasty-discover as a library dependency
-- to your test component in the cabal file.
-- The instance defined should not be an orphaned instance.  A future version of
-- tasty-discover may choose to define orphaned instances for popular test libraries.
import Test.Tasty (testCase)
import Test.Tasty.Discover (TestCase(..), descriptionOf)

data CustomTest = CustomTest String Assertion

instance Tasty CustomTest where
  tasty info (CustomTest prefix act) =
    pure $ testCase (prefix ++ descriptionOf info) act

tasty_myTest :: CustomTest
tasty_myTest = CustomTest "Custom: " $ pure ()

-- Tasty TestTree
test_multiplication :: [TestTree]
test_multiplication = [testProperty "One is identity" $ \(a :: Int) -> a * 1 == a]

-- Tasty IO TestTree
test_generateTree :: IO TestTree
test_generateTree = do
  input <- pure "Some input"
  pure $ testCase input $ pure ()

-- Tasty IO [TestTree]
test_generateTrees :: IO [TestTree]
test_generateTrees = do
  inputs <- pure ["First input", "Second input"]
  pure $ map (\s -> testCase s $ pure ()) inputs

Customise Discovery

You configure tasty-discover by passing options to the test driver file.

No Arguments

Example: {-# OPTIONS_GHC -F -pgmF tasty-discover -optF --debug #-}

  • –debug: Output the contents of the generated module while testing.
  • –tree-display: Display the test output results hierarchically.

With Arguments

Example: {-# OPTIONS_GHC -F -pgmF tasty-discover -optF --modules="*CustomTest.hs" #-}

  • –modules: Which test modules to discover (with glob pattern).
  • –search-dir: Where to look for tests. This is a directory relative to the location of the source file. By default, this is the directory of the source file.”
  • –ignores: Which test modules to ignore (with glob pattern).
  • –generated-module: The name of the generated test module.
  • –ingredient: Tasty ingredients to add to your test runner.
  • –inplace: Has the generated code written to the source file.

It is also possible to override tasty test options with -optF:

{-# OPTIONS_GHC -F -pgmF tasty-discover -optF --hide-successes #-}

Example Project

See the testing for this package for a fully configured example.

Change Log

Please see the for the latest changes.

We try to keep tagged releases in our release process, if you care about that.

Deprecation Policy

If a breaking change is implemented, you’ll see a major version increase, an entry in the change log and a compile-time error with a deprecation warning and clear instructions on how to upgrade. Please do complain if we’re doing this too much.


All contributions welcome! The continuous integration suite is pretty comprehensive, so just get hacking and add a test case - there are plenty of examples, so this should be simple - and I’ll get to review your change ASAP.

Frequently Asked Questions

Deleting Tests Breaks The Test Run

This is a known limitation and has been reported. No fix is planned unless you have time.

Please see #145 for more information.


If you’re interested in helping maintain this package, please let @newhoggy know!

It doesn’t take much time (max ~3 hours a month) and all we need to do is:

  • Triage issues that are raised.
  • Review pull requests from contributors.
  • Fix bugs when present.
  • Make releases.
  • Manage bounds issues on Stackage.

You can create an issue or drop him a line at lukewm AT riseup DOT NET.


Thanks to hspec-discover and tasty-auto for making this possible.

A huge thanks to the growing list of contributors.


Change Log

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Semantic Versioning.

5.0.0 [2022-07-08]

  • Fix tasty-hedgehog testProperty deprecation warning

4.2.4 [2022-05-22]

  • Support for custom test libraries
  • Version module
  • Deduplicate imports in generated code
  • Rename library directory to src
  • Move existing library modules to Test.Discover.Internal

4.2.3 [2022-05-21]

  • Added --search-dir DIR option
  • Adds an --in-place flag to write the generated driver to the source file.

4.2.1 [2018-06-06]


4.2.0 [2018-03-03]


  • Actually support scprop_ prefixed SmallCheck test cases (see issue #140).

4.1.5 [2018-02-26]


  • Fixed multi-byte string issue (see pull request #138).

4.1.4 [2018-02-25]


  • Windows OS continuous integration build (see pull request #136).


  • Test failure related to path handling on Windows OS (see pull request #136).
  • Resolved upstream tasty-hedgehog nightly blocking issue (see issue #131).

4.1.3 [2018-01-01]


  • Re-enable on Stackage due to tasty/tasty-hedgehog failure (see issue #132).

4.1.2 [2017-12-19]


  • Escaping issues for the Windows platform (see issue #124).

4.1.1 [2017-09-26]


  • Incorrect test case doing bad comparison (see issue #123).

4.1.0 [2017-09-26]


  • Find tests recursively in test directory. (see pull request #122).


  • Add ability to override tasty arguments (see pull request #120).

4.0.0 [2017-09-01]


  • Deprecated --[no-]module-suffix for --modules (see pull request #117).
  • Deprecated --ignore-module for --ignores (see pull request #117).


  • tasty-hedgehog is now a supported test library.


  • case_ prefixes have been removed.

3.0.2 [2017-06-05]


  • Make upper bounds for dependencies looser.
  • Fix typo in option documentation.


  • Remove TOC, the hyperlinks weren’t working on Hackage.

3.0.1 [2017-06-04]


  • Fixed rendering for Hackage (see pull request #106).


  • Add missing –tree-display documentation note (see pull request #107).

3.0.0 [2017-06-03]


  • Add –tree-display configuration option (see pull request #103).


  • Deprecate case_ in favour of unit_ for HUnit test cases (see pull request #97).


  • Correctly handle sub-directories when using –no-module-suffix (see pull request #102).

2.0.3 [2017-04-13]


  • Make the Cabal description more clear for Hackage.

2.0.2 [2017-04-13]


  • and included for Hackage (see pull request #96).
  • Re-add stylish-haskell automated checking (see pull request #88).

2.0.1 [2017-03-18]


  • Fix flaky test comparison (see pull request #86).


  • Remove the Test.Tasty.Type module (see pull request #83).

2.0.0 [2017-03-15]


  • Add new hpack format.
  • Add generator style test discovery from tasty-auto.
  • Add new configuration options: debug, ingredients and module name.
  • Add unit tests for all functionality.


  • Re-license to MIT.


  • RTD documentation.
  • TemplateHaskell dependency
  • Example project and integration test project.


  • Move all tests into test folder.

1.1.0 [2017-01-19]


  • Add –ignore-module configuration option.

1.0.1 [2017-11-13]


  • Add Cabal and Documentation testing on Travis CI.


  • Include missing extra-source-files.
  • Slim down and mark as GPL-3 in Cabal file.

1.0.0 [2016-11-04]


  • Add documentation on RTD.
  • Release on Hackage and Stackage.

0.0.3 [2016-09-20]


  • –no-module-suffix configuration option.

0.0.2 [2016-02-20]


  • –module-suffix configuration option.

0.0.1 [2016-02-13]

  • tasty-discover initial release.