function unifiedDiff(actual, expected) {
    var indent = '      ';
    function cleanUp(line) {
      if (line[0] === '+') {
        return indent + colorLines('diff added', line);
      }
      if (line[0] === '-') {
        return indent + colorLines('diff removed', line);
      }
      if (line.match(/@@/)) {
        return '--';
      }
      if (line.match(/\\ No newline/)) {
        return null;
      }
      return indent + line;
    }
    function notBlank(line) {
      return typeof line !== 'undefined' && line !== null;
    }
    var msg = diff.createPatch('string', actual, expected);
    var lines = msg.split('\n').splice(5);
    return (
      '\n      ' +
      colorLines('diff added', '+ expected') +
      ' ' +
      colorLines('diff removed', '- actual') +
      '\n\n' +
      lines.map(cleanUp).filter(notBlank).join('\n')
    );
  }
Returns unified diff between two strings with coloured ANSI output.

@private
@param {String} actual
@param {String} expected
@return {string} The diff.