make inline metadata value clearer

test/cpp/end2end/end2end_test.cc

@@ -1359,7 +1359,7 @@ TEST_P(SecureEnd2endTest, AuthMetadataPluginValueFailure) {
       MetadataCredentialsFromPlugin(std::unique_ptr<MetadataCredentialsPlugin>(
           new TestMetadataCredentialsPlugin(
               TestMetadataCredentialsPlugin::kGoodMetadataKey,
-              "With binary \n data", false, true))));
+              "With illegal \n value.", false, true))));
   request.set_message("Hello");
 
   Status s = stub_->Echo(&context, request, &response);