How to add a struct to a vector from another class?

I am student, and I am trying to build a project. My program is throwing an error while accessing the vector. The size of the vector is 1, but when I call RenderQueue.front it throws an error:

front() called on empty vector.

My code is below:

global.h

struct RenderStruct {
    std::function<void()> testfunction1;
    std::function<void()> testfunction2;
};
static std::vector<RenderStruct> RenderQueue;

Test.h

class test
{
public:
    static void add_to_queue();
};

Test.cpp

void test::add_to_queue()
{
        std::function<void()> testfunction1 = [&]()
        {
            std::cout << "First Function Working" << std::endl;
        };
        std::function<void()> testfunction2 = [&]()
        {
            std::cout << "Second Function Working" << std::endl;
        };
        RenderQueue.push_back({testfunction1, testfunction2}); 
};

Main.cpp

int main()
{
    test::add_to_queue();
    auto front = RenderQueue.front();

    front.testfunction();
    front.testfunction2();
};