[Console] fix NullOutput

It should not extend from abstract Output class because than it inherits the useless constructor arguments and applies formatting in write() needlessly.

src/Symfony/Component/Console/Output/NullOutput.php

@@ -11,24 +11,83 @@
 
 namespace Symfony\Component\Console\Output;
 
+use Symfony\Component\Console\Formatter\OutputFormatter;
+use Symfony\Component\Console\Formatter\OutputFormatterInterface;
+
 /**
  * NullOutput suppresses all output.
  *
  *     $output = new NullOutput();
  *
  * @author Fabien Potencier <fabien@symfony.com>
+ * @author Tobias Schultze <http://tobion.de>
  *
  * @api
  */
-class NullOutput extends Output
+class NullOutput implements OutputInterface
 {
     /**
-     * Writes a message to the output.
-     *
-     * @param string  $message A message to write to the output
-     * @param Boolean $newline Whether to add a newline or not
+     * {@inheritdoc}
      */
-    protected function doWrite($message, $newline)
+    public function setFormatter(OutputFormatterInterface $formatter)
     {
+        // do nothing
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getFormatter()
+    {
+        // to comply with the interface we must return a OutputFormatterInterface
+        return new OutputFormatter();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setDecorated($decorated)
+    {
+        // do nothing
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isDecorated()
+    {
+        return false;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setVerbosity($level)
+    {
+        // do nothing
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getVerbosity()
+    {
+        return self::VERBOSITY_QUIET;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function writeln($messages, $type = 0)
+    {
+        // do nothing
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function write($messages, $newline = false, $type = 0)
+    {
+        // do nothing
     }
 }

src/Symfony/Component/Console/Tests/Output/NullOutputTest.php

@@ -25,6 +25,7 @@ class NullOutputTest extends \PHPUnit_Framework_TestCase
         $buffer = ob_get_clean();
 
         $this->assertSame('', $buffer, '->write() does nothing (at least nothing is printed)');
+        $this->assertFalse($output->isDecorated(), '->isDecorated() returns false');
     }
 
     public function testVerbosity()