@Test
public void succeedsWhenHeadersContainSubjectId() {

    final String subjectId = "nginx:first";
    final DittoHeaders validHeaders = DittoHeaders.newBuilder()
            .authorizationContext(AuthorizationContext.newInstance(DittoAuthorizationContextType.UNSPECIFIED,
                    AuthorizationSubject.newInstance(subjectId), AuthorizationSubject.newInstance("nginx:second")))
            .build();
    final String actualSubjectId = underTest.apply(validHeaders);
    assertThat(actualSubjectId).isEqualTo(subjectId);
}