How to make a required / not required one field depending on value of second field (Drupal in registration form)

Question

Below is an example of code that makes the first field not required in the form

<?php
    function мой_модуль_form_alter(&$form, &$form_state, $form_id){
    $form['field_website']['und'][0]['#required'] = FALSE;
    }
?>

---

$form['test']['und'][0]['value']=test;

But I need to check the content in the second field after sending the form, and if it coincides with the value of "test", then the first field became not required.

if($form['test']['und'][0]['value']=='test'){
    $form['field_website']['und'][0]['#required'] = FALSE;
}

Answer 1

Use Conditional Fields module.