feat: tests for the rendering/parsing

src/Language/Brainfuck/Instruction.hs

@@ -1,7 +1,13 @@
 {-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE InstanceSigs #-}
 module Language.Brainfuck.Instruction (Instruction(..)) where
 
 import Data.Vector ( Vector )
+import Test.QuickCheck.Gen (Gen)
+import Test.QuickCheck.Arbitrary (Arbitrary (arbitrary))
+import Test.QuickCheck.Instances.Vector ()
+
+import qualified Test.QuickCheck.Gen as Gen
 
 data Instruction
   = Increment
@@ -12,3 +18,20 @@ data Instruction
   | PutByte
   | Loop (Vector Instruction)
   deriving stock (Show, Eq)
+
+instance Arbitrary Instruction where
+  arbitrary :: Gen Instruction
+  arbitrary = Gen.oneof $
+    [ pure Increment
+    , pure Decrement
+    , pure MoveLeft
+    , pure MoveRight
+    , pure ReadByte
+    , pure PutByte
+    , Loop <$> reduceSize 8 arbitrary
+    ]
+    where
+      reduceSize d g = Gen.sized $ \ s -> Gen.resize (s `div` d) g
+
+-- >>> Gen.generate (Gen.resize 30 arbitrary) :: IO [Instruction]
+-- [MoveLeft,Decrement,PutByte,Decrement,Decrement,Increment,ReadByte,MoveLeft,Increment,Loop [],MoveRight,Increment,Increment,Loop [],MoveLeft,Loop [],MoveRight,ReadByte,ReadByte,MoveLeft,Decrement,MoveRight,MoveLeft,Loop [PutByte,Increment,Loop []],Decrement]