@Test
public void unique_id_for_each_message_is_logged() {

    String message = "message1";
    int messageId = System.identityHashCode(message);
    logger.onMessageSent(message);
    String output = this.output.toString();
    assertThat(output, containsString(Integer.toHexString(messageId)));
    assertThat(output).matches("(?s).* 0x[0-9a-f]{8} .*");
}