protected function getHandler()
 {
     $resp = new \stdClass();
     $resp->http_response_code = 200;
     $this->mailgun = $this->prophesize(Mailgun::class);
     $this->mailgun->sendMessage(Argument::cetera())->willReturn($resp);
     return new MailgunHandler($this->mailgun->reveal(), 'www.example.org', 'default', 'mailgun');
 }