Add missing test for schema parser

Author: Cito

README.md

@@ -16,7 +16,7 @@ The current version 3.0.1 of GraphQL-core is up-to-date
 with GraphQL.js version 14.5.8.
 
 All parts of the API are covered by an extensive test suite
-of currently 1990 unit tests.
+of currently 1991 unit tests.
 
 
 ## Documentation

tests/language/test_schema_parser.py

@@ -573,6 +573,11 @@ def union_fails_with_leading_double_pipe():
             "union Hello = || Wo | Rld", "Expected Name, found |", (1, 16)
         )
 
+    def union_fails_with_double_pipe():
+        assert_syntax_error(
+            "union Hello = Wo || Rld", "Expected Name, found |", (1, 19)
+        )
+
     def union_fails_with_trailing_pipe():
         assert_syntax_error(
             "union Hello = | Wo | Rld |", "Expected Name, found <EOF>", (1, 27)