How do I get a return value using call by reference?

When I call a private function with call by reference like below code,

I only get a empty value,

Please let me know how to properly pass an argument.

with Isolator++

// function

int Auth::getName(string& name)

{

    name = "hello";

    return 1;

}

// main

std::string passed = "hi";

int ret;

ISOLATOR_INVOKE_FUNCTION(ret, getName, passed);

ASSERT_EQ(passed, "hello");

passed is empty string