@Test
public void toJsonReturnsExpected() {

    final RetrieveThingDefinition underTest =
            RetrieveThingDefinition.of(TestConstants.Thing.THING_ID, TestConstants.EMPTY_DITTO_HEADERS);
    final JsonObject actualJson = underTest.toJson(KNOWN_SCHEMA_VERSION, FieldType.regularOrSpecial());
    assertThat(actualJson).isEqualTo(KNOWN_JSON);
}