Test absence of name clash between type names and directives

Replicates graphql/graphql-js@732c90f

Author: Cito

README.md

@@ -13,7 +13,7 @@ a query language for APIs created by Facebook.
 
 The current version 1.0.0rc2 of GraphQL-core-next is up-to-date with GraphQL.js
 version 14.0.0rc2. All parts of the API are covered by an extensive test
-suite of currently 1529 unit tests.
+suite of currently 1530 unit tests.
 
 
 ## Documentation

tests/utilities/test_build_ast_schema.py

@@ -885,6 +885,20 @@ def unknown_subscription_type():
         assert msg == (
             "Specified subscription type 'Awesome' not found in document.")
 
+    def does_not_consider_directive_names():
+        body = dedent("""
+            schema {
+              query: Foo
+            }
+
+            directive @ Foo on QUERY
+            """)
+        doc = parse(body)
+        with raises(TypeError) as exc_info:
+            build_ast_schema(doc)
+        msg = str(exc_info.value)
+        assert msg == "Specified query type 'Foo' not found in document."
+
     def does_not_consider_operation_names():
         body = dedent("""
             schema {