### Question:
Region { public String getDomain() { return domain; } Region(final String name, final String domain); static Region getRegion(Regions region); static Region getRegion(String regionString); String getName(); String getDomain(); String getServiceEndpoint(String serviceName); boolean isServiceSupported(String serviceName); boolean hasHttpsEndpoint(String serviceName); boolean hasHttpEndpoint(String serviceName); T createClient(Class<T> serviceClass,
            AWSCredentialsProvider credentials,
            ClientConfiguration config); @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void testDefaultDomain() { final String serviceName = "s3"; assertEquals("empty domain", DEFAULT_DOMAIN, new Region(serviceName, "").getDomain()); assertEquals("null domain", DEFAULT_DOMAIN, new Region(serviceName, null).getDomain()); }