Move code to Internal module and add tests

hcat.cabal

@@ -6,7 +6,7 @@ cabal-version: 1.12
 
 name:           hcat
 version:        0.0.1.0
-description:    Hcat example from the book 'Effective Haskell'
+description:    HCat example from the book 'Effective Haskell'
 author:         Alexander Kobjolke
 maintainer:     alex@jakalx.net
 copyright:      Alexander Kobjolke 2023
@@ -18,11 +18,16 @@ extra-source-files:
 library
   exposed-modules:
       HCat
+      HCat.Internal
   other-modules:
       Paths_hcat
   hs-source-dirs:
       src
-  ghc-options: -Wall -Wunused-packages
+  default-extensions:
+      GHC2021
+      BlockArguments
+      OverloadedStrings
+  ghc-options: -Wall -Wunused-packages -fdefer-typed-holes
   build-depends:
       base >=4.13 && <5
     , text
@@ -34,9 +39,39 @@ executable hcat
       Paths_hcat
   hs-source-dirs:
       app
-  ghc-options: -Wall -Wunused-packages
+  default-extensions:
+      GHC2021
+      BlockArguments
+      OverloadedStrings
+  ghc-options: -Wall -Wunused-packages -fdefer-typed-holes
   build-depends:
       base >=4.13 && <5
     , hcat
     , text
   default-language: GHC2021
+
+test-suite spec
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      HCatSpec
+      Paths_hcat
+  hs-source-dirs:
+      test
+  default-extensions:
+      GHC2021
+      BlockArguments
+      OverloadedStrings
+  ghc-options: -Wall -Wunused-packages -fdefer-typed-holes
+  cpp-options: -DTEST
+  build-tool-depends:
+      hspec-discover:hspec-discover
+  build-depends:
+      QuickCheck
+    , base >=4.13 && <5
+    , hcat
+    , hspec
+    , quickcheck-instances
+    , quickcheck-text
+    , text
+  default-language: Haskell2010