use Mojolicious::Lite;

get '/test' => sub {
    my $c = shift;

    $c->render( text => $c->url_for('test')->to_abs );  # works
};

helper route_url => sub {
    my $c = shift;

    app->log->info( $c->url_for('test')->to_abs);  # generates errors
};

Mojo::IOLoop->timer( 3 => sub { app->route_url } );   # give things time to simmer down

app->start;