Menu callback: displays the 'Edit exiisting test_entity' form.
function field_test_entity_edit(TestEntity $entity) {
drupal_set_title(t('test_entity @ftid revision @ftvid', array(
'@ftid' => $entity->ftid,
'@ftvid' => $entity->ftvid,
)), PASS_THROUGH);
return entity_get_form($entity);
}