@Override
  public Map<Headers, String> getHeaders() {
    return Collections.unmodifiableMap(headers);
  }
@Test
  void testUnModifiableHeaders() {
    final var message = new SimpleMessage();
    final var headers = message.getHeaders();
    assertThrows(UnsupportedOperationException.class, () -> headers.put(Message.Headers.SENDER, "test"));
  }