public function testsetFilterImageProxyCallback()
 {
     $config = new Config();
     $config->setFilterImageProxyCallback(function ($image_url) {
         $key = hash_hmac('sha1', $image_url, 'secret');
         return 'https://mypublicproxy/' . $key . '/' . rawurlencode($image_url);
     });
     $f = Filter::html('<p>Image <img src="/image.png" alt="My Image"/></p>', 'http://foo');
     $f->setConfig($config);
     $this->assertEquals('<p>Image <img src="https://mypublicproxy/4924964043f3119b3cf2b07b1922d491bcc20092/' . rawurlencode('http://foo/image.png') . '" alt="My Image"/></p>', $f->execute());
 }