Parse yaml before working on it (#114)

test-setup/package.yaml

@@ -10,4 +10,8 @@ executables:
     source-dirs: src
     ghc-options: -Wall
     dependencies:
+      - aeson
       - directory
+      - lens
+      - lens-aeson
+      - yaml

test-setup/src/Main.hs

@@ -1,3 +1,6 @@
+{-# LANGUAGE OverloadedLists #-}
+{-# LANGUAGE OverloadedStrings #-}
+
 {-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
 module Main (main) where
 import Data.List (findIndex, isInfixOf)
@@ -6,6 +9,10 @@ import System.Environment (getArgs)
 import Control.Arrow ((>>>))
 import Control.Monad (when)
 import System.Directory (copyFile)
+import Data.Aeson.Lens (key, _Array)
+import Control.Lens ((%~))
+import Data.Yaml ( decodeFileThrow, encodeFile )
+import qualified Data.Yaml as Yaml
 
 main :: IO ()
 main = do
@@ -34,10 +41,11 @@ modifyTests inputDir = do
   {-# HLINT ignore "Use null" #-}
   when (length newTestFileData > 0) $ writeFile testFile (unlines newTestFileData)
 
-  -- Add aeson, aeson-pretty, bytestring, hspec-core, stm and text packages to `tests` section of 
-  -- package.yaml.
-  -- (assumes that the tests.test.dependencies is the last item in package.yaml!)
-  appendFile packageFile "      - aeson\n      - aeson-pretty\n      - bytestring\n      - hspec-core\n      - stm\n      - text\n"
+  -- Add aeson, aeson-pretty, bytestring, hspec-core, stm and text packages to `tests` section of package.yaml.
+  let missingDependencies = ["aeson", "aeson-pretty", "bytestring", "hspec-core", "stm", "text"]
+      addDepependencies = key "tests" . key "test" . key "dependencies" . _Array %~ (<> missingDependencies)
+  originalYaml <- decodeFileThrow packageFile :: IO Yaml.Value
+  encodeFile packageFile (addDepependencies originalYaml)
 
   -- Copy our custom hspec formatter into the input code directory so it can be used
   copyFile hspecFormatterPath (inputDir ++ "/test/HspecFormatter.hs")