Retrieves the FieldInstance object for the given field and returns the editor that Edit selects.
protected function getSelectedEditor($items, $field_name, $view_mode = 'default') {
$options = entity_get_display('entity_test', 'entity_test', $view_mode)
->getComponent($field_name);
$field_instance = field_info_instance('entity_test', $field_name, 'entity_test');
return $this->editorSelector
->getEditor($options['type'], $field_instance, $items);
}