Webiny\Component\Mailer\Bridge\SwiftMailer\Message::getHeaders PHP Method

    public function getHeaders()
    {
        $swiftHeaders = $this->message->getHeaders()->listAll();
        $headers = [];
        foreach ($swiftHeaders as $headerName) {
            $headers[$headerName] = $this->getHeader($headerName);
        }
        return $headers;
    }

 /**
  * @dataProvider messageProvider
  *
  * @param Message $message
  *
  */
 public function testAddHeader($message)
 {
     $message->addHeader('test', 'value');
     $this->assertSame('value', $message->getHeader('test'));
     $this->assertArrayHasKey('test', $message->getHeaders());
 }