Validate directives are unique per location

tests/Language/GraphQL/AST/LexerSpec.hs

@@ -77,7 +77,7 @@ spec = describe "Lexer" $ do
             parse spread "" "..." `shouldParse` "..."
             parse colon "" `shouldSucceedOn` ":"
             parse equals "" "=" `shouldParse` "="
-            parse at "" "@" `shouldParse` "@"
+            parse at "" `shouldSucceedOn` "@"
             runBetween brackets `shouldSucceedOn` "[]"
             runBetween braces `shouldSucceedOn` "{}"
             parse pipe "" "|" `shouldParse` "|"

tests/Language/GraphQL/AST/ParserSpec.hs

@@ -128,7 +128,7 @@ spec = describe "Parser" $ do
         parse document "" `shouldSucceedOn` [r|extend schema { query: Query }|]
 
     it "parses schema extension with an operation type and directive" $
-        let newDirective = Directive "newDirective" []
+        let newDirective = Directive "newDirective" [] $ Location 1 15
             schemaExtension = SchemaExtension
                 $ SchemaOperationExtension [newDirective]
                 $ OperationTypeDefinition Query "Query" :| []

tests/Language/GraphQL/ValidateSpec.hs

@@ -428,3 +428,16 @@ spec =
                     , locations = [AST.Location 4 34, AST.Location 4 54]
                     }
              in validate queryString `shouldBe` Seq.singleton expected
+
+        it "rejects more than one directive per location" $ do
+            let queryString = [r|
+              query ($foo: Boolean = true, $bar: Boolean = false) {
+                field @skip(if: $foo) @skip(if: $bar)
+              }
+            |]
+                expected = Error
+                    { message =
+                        "There can be only one directive named \"skip\"."
+                    , locations = [AST.Location 3 23, AST.Location 3 39]
+                    }
+             in validate queryString `shouldBe` Seq.singleton expected