### Question:
NatService { public static NatMethod autoDetectNatMethod(final NatMethodDetector... natMethodDetectors) { return Arrays.stream(natMethodDetectors) .flatMap(natMethodDetector -> natMethodDetector.detect().stream()) .findFirst() .orElse(NatMethod.NONE); } NatService(final Optional<NatManager> natManager, final boolean fallbackEnabled);  NatService(final Optional<NatManager> natManager); boolean isNatEnvironment(); void ifNatEnvironment(
      final NatMethod natMethod, final Consumer<? super NatManager> action); NatMethod getNatMethod(); Optional<NatManager> getNatManager(); void start(); void stop(); String queryExternalIPAddress(final String fallbackValue); String queryLocalIPAddress(final String fallbackValue); Optional<NatPortMapping> getPortMapping(
      final NatServiceType serviceType, final NetworkProtocol networkProtocol); static NatMethod autoDetectNatMethod(final NatMethodDetector... natMethodDetectors);  }### Answer:
@Test public void givenOneAutoDetectionWorksWhenAutoDetectThenReturnCorrectNatMethod() { final NatMethod natMethod = NatService.autoDetectNatMethod(() -> Optional.of(NatMethod.UPNP)); assertThat(natMethod).isEqualTo(NatMethod.UPNP); }
@Test public void givenNoAutoDetectionWorksWhenAutoDetectThenReturnEmptyNatMethod() { final NatMethod natMethod = NatService.autoDetectNatMethod(Optional::empty); assertThat(natMethod).isEqualTo(NatMethod.NONE); }