Validate all variables are defined

tests/Language/GraphQL/AST/EncoderSpec.hs

@@ -122,7 +122,8 @@ spec = do
     describe "definition" $
         it "indents block strings in arguments" $
             let location = Location 0 0
-                arguments = [Argument "message" (String "line1\nline2") location]
+                argumentValue = Node (String "line1\nline2") location
+                arguments = [Argument "message" argumentValue location]
                 field = Field Nothing "field" arguments [] [] location
                 operation = DefinitionOperation
                     $ SelectionSet (pure $ FieldSelection field) location

tests/Language/GraphQL/ValidateSpec.hs

@@ -471,3 +471,24 @@ spec =
                     , locations = [AST.Location 2 34]
                     }
              in validate queryString `shouldBe` Seq.singleton expected
+
+        it "rejects undefined variables" $
+            let queryString = [r|
+              query variableIsNotDefinedUsedInSingleFragment {
+                dog {
+                  ...isHousetrainedFragment
+                }
+              }
+
+              fragment isHousetrainedFragment on Dog {
+                isHousetrained(atOtherHomes: $atOtherHomes)
+              }
+            |]
+                expected = Error
+                    { message =
+                        "Variable \"$atOtherHomes\" is not defined by \
+                        \operation \
+                        \\"variableIsNotDefinedUsedInSingleFragment\"."
+                    , locations = [AST.Location 9 46]
+                    }
+             in validate queryString `shouldBe` Seq.singleton expected