public function testFilterFunction()
{
$filter = $this->getMock('Assetic\\Filter\\FilterInterface');
$this->fm->expects($this->once())->method('get')->with('some_filter')->will($this->returnValue($filter));
$this->twig->addExtension(new AsseticExtension($this->factory, array('some_func' => array('filter' => 'some_filter', 'options' => array('output' => 'css/*.css')))));
$xml = $this->renderXml('function.twig');
$this->assertEquals(1, count($xml->asset));
$this->assertStringEndsWith('.css', (string) $xml->asset[0]['url']);
}