Add Semigroup and Monoid instances for Description

tests/Language/GraphQL/AST/DocumentSpec.hs

@@ -18,3 +18,9 @@ spec = do
                     ]
                 expected = "{ field1: 1.2, field2: null }"
              in show object `shouldBe` expected
+
+    describe "Description" $
+        it "keeps content when merging with no description" $
+            let expected = Description $ Just "Left description"
+                actual = expected <> Description Nothing
+             in actual `shouldBe` expected

tests/Language/GraphQL/AST/EncoderSpec.hs

@@ -180,7 +180,7 @@ spec = do
             let actual = operationType pretty Full.Mutation
              in actual `shouldBe` "mutation"
 
-    describe "typeSystemDefinition" $
+    describe "typeSystemDefinition" $ do
         it "produces a schema with an indented operation type definition" $
             let queryType = Full.OperationTypeDefinition Full.Query "QueryRootType"
                 mutationType = Full.OperationTypeDefinition Full.Mutation "MutationType"
@@ -194,3 +194,10 @@ spec = do
                 |] '\n'
                 actual = typeSystemDefinition pretty definition'
              in actual `shouldBe` expected
+
+        it "encodes a scalar type definition" $
+            let uuidType = Full.ScalarTypeDefinition mempty "UUID" mempty
+                definition' = Full.TypeDefinition uuidType
+                expected = "scalar UUID"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected