Fix CliCredentials reference
diff --git a/test/cpp/util/grpc_tool_test.cc b/test/cpp/util/grpc_tool_test.cc
index 1d790c6..edb66b7 100644
--- a/test/cpp/util/grpc_tool_test.cc
+++ b/test/cpp/util/grpc_tool_test.cc
@@ -109,7 +109,7 @@
 
   void ShutdownServer() { server_->Shutdown(); }
 
-  void ExitWhenError(int argc, const char** argv, const CliCredentials cred,
+  void ExitWhenError(int argc, const char** argv, const CliCredentials& cred,
                      GrpcToolOutputCallback callback) {
     int result = GrpcToolMainLib(argc, argv, cred, callback);
     if (result) {