Appendin POST variable to form test

I have a form that uses Angular JS to create and populate a hidden field. Can I append this to in Laravel's unit testing? If I do:

    $this->visit('/page')
        ->type('Yo Momma', 'name')
        ->type(123, 'hidden_field_name')
        ->press('Do It')

it can't find the field as it's created by JavaScript. Thanks.