@Test
public void getThingIdAlthoughItIsNotSet() {

    final MessageHeaders underTest = ImmutableMessageHeaders.of(DittoHeaders.empty());
    assertThatExceptionOfType(IllegalStateException.class)
            .isThrownBy(underTest::getThingEntityId)
            .withMessage("MessageHeaders did not contain a value for key <%s>!",
                    MessageHeaderDefinition.THING_ID.getKey())
            .withNoCause();
}