The test-fixture package

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Dependencies base (>=4.7 && <5), data-default-class, exceptions, haskell-src-exts, haskell-src-meta, mtl, template-haskell (>=2.10 && <2.13), th-orphans, transformers [details]
License BSD3
Copyright 2016 CJ Affiliate by Conversant
Author Joe Vargas
Category Test
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Source repo head: git clone
Uploaded Mon Oct 30 23:25:49 UTC 2017 by lexi_lambda
Distributions LTSHaskell:, NixOS:, Stackage:, openSUSE:
Downloads 2224 total (89 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by rule of succession]
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Status Docs available [build log]
Last success reported on 2017-10-30 [all 1 reports]
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test-fixture Build Status

The test-fixture package is a Haskell library that makes it possible to easily write deterministic unit tests for code that encapsulates effects into monadic typeclasses. For example, given some typeclasses used to encapsulate effects:

class Monad m => MonadDB m where
  fetchRecord :: DBRecord a => Id a -> m (Either DBError a)
  insertRecord :: DBRecord a => a -> m (Either DBError (Id a))

class Monad m => MonadHTTP m where
  sendRequest :: HTTPRequest -> m (Either HTTPError HTTPResponse)

One can write IO instances to run the actual code in a real environment:

instance MonadDB IO where
  fetchRecord = Postgres.fetchRecord
  insertRecord = Postgres.insertRecord

instance MonadHTTP IO where
  sendRequest = sendRequestIO

Then use those typeclasses to implement some sort of side-effectful function:

sendAndFetch :: (MonadDB m, MonadHTTP m, DBRecord a)
             => HTTPRequest -> m (Either AppError a)
sendAndFetch = ...

Testing this function might be difficult because of all the different possible combinations of scenarios that must be considered. Creating lots of different monads and instances for each case can be boilerplate-heavy and tedious. Using test-fixture, the boilerplate is unnecessary:

mkFixture "Fixture" [ts| MonadDB, MonadHTTP |]

spec = describe "sendAndFetch" $ do
  it "returns a record when the http request and db fetch are successful" $ do
    let (fixture :: Monad m => Fixture m) = def
      { _fetchRecord = \_ -> return $ Right procureRecord
      , _sendRequest = \_ -> return $ Right responseOk
    let result = unTestFixture (sendAndFetch simpleRequest) fixture
    result `shouldBe` Right (User "")

  it "returns an error when the http request is not successful" $ do
    let (fixture :: Monad m => Fixture m) = def
      { _fetchRecord = \_ -> return $ Right procureRecord
      , _sendRequest = \_ -> return $ Left errorNotAuthorized
    let result = unTestFixture (sendAndFetch simpleRequest) fixture
    result `shouldBe` Left (AppHTTPError errorNotAuthorized)

For more information and a more complete explanation, see the documentation on Hackage.