Test Form API protections against input forgery.
function testInputForgery() {
$this
->drupalGet('form-test/input-forgery');
$checkbox = $this
->xpath('//input[@name="checkboxes[two]"]');
$checkbox[0]['value'] = 'FORGERY';
$this
->drupalPost(NULL, array(
'checkboxes[one]' => TRUE,
'checkboxes[two]' => TRUE,
), t('Submit'));
$this
->assertText('An illegal choice has been detected.', 'Input forgery was detected.');
}