Form submit handler for the partial validation submit button.
function form_test_limit_validation_errors_form_partial_submit($form, $form_state) {
// The title has not been validated, thus its value - in case of the test case
// an empty string - may not be set.
if (!isset($form_state['values']['title']) && isset($form_state['values']['test'])) {
drupal_set_message('Only validated values appear in the form values.');
}
}