feat: tests for the rendering/parsing

test/Arbitrary/InvalidBrainfuckText.hs

@@ -0,0 +1,26 @@
+{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE DerivingStrategies #-}
+module Arbitrary.InvalidBrainfuckText (InvalidBrainfuckText(..)) where
+
+import Data.Text (Text)
+import Test.QuickCheck.Gen (Gen)
+import Test.QuickCheck.Arbitrary (Arbitrary (arbitrary))
+
+import qualified Data.Text as Text
+import qualified Test.QuickCheck.Gen as Gen
+import qualified Arbitrary.ValidBrainfuckText as ValidBrainfuckText
+
+newtype InvalidBrainfuckText = InvalidBrainfuckText { get :: Text }
+  deriving stock Show
+
+instance Arbitrary InvalidBrainfuckText where
+  arbitrary :: Gen InvalidBrainfuckText
+  arbitrary = do
+    validText <- ValidBrainfuckText.get <$> arbitrary
+
+    index <- Gen.choose (0, Text.length validText)
+    badBrace <- Gen.oneof $ map pure "[]"
+    let (prefix, suffix) = Text.splitAt index validText
+    
+    pure . InvalidBrainfuckText $ Text.concat [prefix, Text.singleton badBrace, suffix]
+