Add an Arbitrary instance for Category.

src/Category.hs

@@ -3,6 +3,7 @@ module Category where
 import Prologue
 import Data.Hashable
 import Data.String
+import Test.QuickCheck
 
 -- | A standardized category of AST node. Used to determine the semantics for
 -- | semantic diffing and define comparability of nodes.
@@ -35,3 +36,21 @@ data Category
 -- Instances
 
 instance Hashable Category
+
+instance Arbitrary Category where
+  arbitrary = oneof
+    [ pure Program
+    , pure Error
+    , pure BinaryOperator
+    , pure DictionaryLiteral
+    , pure Pair
+    , pure FunctionCall
+    , pure StringLiteral
+    , pure IntegerLiteral
+    , pure SymbolLiteral
+    , pure ArrayLiteral
+    , Other <$> arbitrary
+    ]
+
+  shrink (Other s) = Other <$> shrink s
+  shrink _ = []