public function testSerialize()
 {
     $token = new OAuthToken('token', 'secret');
     $this->assertEquals('oauth_token=token&oauth_token_secret=secret', $token->to_string());
     $token = new OAuthToken('token&', 'secret%');
     $this->assertEquals('oauth_token=token%26&oauth_token_secret=secret%25', $token->to_string());
 }