An answer for https://teratail.com/questions/337667

.editorconfig

[*]
charset = utf-8
end_of_line = lf
insert_final_newline = true
indent_size = 2
indent_style = space

.gitignore

/dist-newstyle/

README.md

An answer for https://teratail.com/questions/337667

cabal.project

packages: .

hie.yaml

cradle:
  cabal:
    - path: "././"
      component: "lib:unit-test-io"

    - path: "././Main.hs"
      component: "unit-test-io:exe:unit-test-io"

    - path: "././UnitTestIO.hs"
      component: "unit-test-io:exe:unit-test-io"

    - path: "././"
      component: "unit-test-io:test:spec"

Main.hs

import qualified UnitTestIO

main :: IO ()
main = UnitTestIO.main

unit-test-io.cabal

cabal-version:       >=1.10
-- Initial package description 'unit-test-io.cabal' generated by 'cabal
-- init'.  For further documentation, see
-- http://haskell.org/cabal/users-guide/

name:                unit-test-io
version:             0.1.0.0
-- synopsis:
-- description:
-- bug-reports:
-- license:
-- license-file:        LICENSE
author:              Kazuki Okamoto
maintainer:          kazuki.okamoto@kakkun61.com
-- copyright:
-- category:
build-type:          Simple
-- extra-source-files:  CHANGELOG.md

library
  exposed-modules:     UnitTestIO
  build-depends:       base >=4.14 && <4.15
  default-language:    Haskell2010

executable unit-test-io
  main-is:             Main.hs
  other-modules:       UnitTestIO
  build-depends:       base >=4.14 && <4.15
  default-language:    Haskell2010

test-suite spec
  type:                exitcode-stdio-1.0
  main-is:             UnitTestIOSpec.hs
  other-modules:       UnitTestIO
  build-depends:       base >=4.14 && <4.15,
                       bytestring,
                       hspec,
                       main-tester
  default-language:    Haskell2010

UnitTestIO.hs

module UnitTestIO (main) where

main :: IO ()
main = interact id

UnitTestIOSpec.hs

{-# LANGUAGE OverloadedStrings #-}

import qualified Data.ByteString as B
import           System.Exit     (ExitCode (ExitSuccess))
import           Test.Hspec      (hspec, it, shouldBe, shouldSatisfy)
import           Test.Main       (captureProcessResult, prExitCode, prStderr,
                                  prStdout, withStdin)
import qualified UnitTestIO

main =
  hspec $ do
    it "hello → hello" $ do
      result <- withStdin "hello" $ captureProcessResult UnitTestIO.main
      prExitCode result `shouldBe` ExitSuccess
      prStderr result `shouldSatisfy` B.null
      prStdout result `shouldBe` "hello"