Custom variables

Please help. Why Spacious theme not working with custom variables?
I add code in function.php

function add_my_var($public_query_vars) {
    $public_query_vars[] = 'test';
    return $public_query_vars;
}
add_filter('query_vars', 'add_my_var');

but url ……/?test=searchword show a Error : “Fatal error: Allowed memory size …”