Google Test and static local variable

I have a method that contains a static unsigned int, so it can return consecutive directory names. Something like:

string MyClass::createDirectory() const
{
    static unsigned int i = 0;
    stringstream ss;
    string directory;
    do
    {
        ++i;
        ss.str("");
        ss << "/" << setfill('0') << setw(6) << i;
        directory = m_rootDirectory + ss.str();

    } while(!m_filesystem->createDirectory((directory)));

    return directory;
}

I know this is pretty naive solution, but it is good enough for now.

But I have encountered problem while writing unit tests - the static variable is incremented between test cases.

Is there a way to reset such variable? Or is changing static method variable to non-static class member my only option?

I'm using Google Test framework.