Author: Sebastian Bergmann (sb@sebastian-bergmann.de)
Author: Kore Nordmann (mail@kore-nordmann.de)
 /**
  * Calculate the unified diff between the original source code and its
  * its mutated form
  *
  * @return string
  */
 public function getDiff()
 {
     $original = $this->_reconstructFromTokens($this->_tokensOriginal);
     $mutated = $this->_reconstructFromTokens($this->_tokensMutated);
     $difference = \Mutagenesis\Utility\Diff::difference($original, $mutated);
     return $difference;
 }