Exclude test if parser doesn't exist

Author: jportner

tests/src/rules/no-duplicates.js

@@ -131,7 +131,7 @@ ruleTester.run('no-duplicates', rule, {
     }),
 
     // These test cases use duplicate import identifiers, which causes a fatal parsing error using ESPREE (default) and TS_OLD.
-    ...[parsers.BABEL_OLD, parsers.TS_NEW].flatMap((parser => [
+    ...[parsers.BABEL_OLD, parsers.TS_NEW].flatMap((parser => !parser ? [] : [
       // #2347: duplicate identifiers should be removed
       test({
         code: "import {a} from './foo'; import { a } from './foo'",