public function testRegisterDatatype()
 {
     DataValueFactory::registerDatatype('_foo', '\\SMW\\FooValue', SMWDataItem::TYPE_NOTYPE, 'FooValue');
     $this->assertEquals('FooValue', DataValueFactory::findTypeLabel('_foo'));
     DataValueFactory::getInstance()->registerDatatype('_foo', '\\SMW\\FooValue', SMWDataItem::TYPE_NOTYPE, 'FooValue');
     $this->assertEquals('FooValue', DataValueFactory::getInstance()->findTypeLabel('_foo'));
 }