public Map<String, V> asMap() {
        return unmodifiableMap;
    }
@Test
    public void testAsMap() {
        DomainNameMapping<String> mapping = new DomainNameMapping<String>("NotFound")
            .add("netty.io", "Netty")
            .add("downloads.netty.io", "Netty-Downloads");

        Map<String, String> entries = mapping.asMap();

        assertEquals(2, entries.size());
        assertEquals("Netty", entries.get("netty.io"));
        assertEquals("Netty-Downloads", entries.get("downloads.netty.io"));
    }