@Test
public void toJsonReturnsExpected() {

    final SendThingMessage<?> underTest =
            SendThingMessage.of(THING_ID, MESSAGE, TestConstants.EMPTY_DITTO_HEADERS);
    final JsonObject actualJson = underTest.toJson(FieldType.regularOrSpecial());
    assertThat(actualJson).isEqualTo(KNOWN_JSON);
}