@Override
    public Optional<ConfigTable> readConfig(Set<String> keys) {
        removeUninterestedKeys(keys);

        registerKeyListeners(keys);

        final ConfigTable table = new ConfigTable();

        configItemKeyedByName.forEach((key, value) -> {
            if (value.isPresent()) {
                table.add(new ConfigTable.ConfigItem(key, value.get()));
            } else {
                table.add(new ConfigTable.ConfigItem(key, null));
            }
        });

        return Optional.of(table);
    }
@Test
    public void shouldUpdateCachesWhenNotified() {
        cacheByKey = new ConcurrentHashMap<>();
        configItemKeyedByName = new ConcurrentHashMap<>();
        Whitebox.setInternalState(register, "cachesByKey", cacheByKey);
        Whitebox.setInternalState(register, "configItemKeyedByName", configItemKeyedByName);

        KVCache cache1 = mock(KVCache.class);
        KVCache cache2 = mock(KVCache.class);

        ArgumentCaptor<ConsulCache.Listener> listener1 = ArgumentCaptor.forClass(ConsulCache.Listener.class);
        ArgumentCaptor<ConsulCache.Listener> listener2 = ArgumentCaptor.forClass(ConsulCache.Listener.class);

        try (MockedStatic<KVCache> kvCacheMockedStatic = mockStatic(KVCache.class)) {
            kvCacheMockedStatic.when(() -> KVCache.newCache(any(), eq("key1"))).thenReturn(cache1);
            kvCacheMockedStatic.when(() -> KVCache.newCache(any(), eq("key2"))).thenReturn(cache2);

            when(register.readConfig(any(Set.class))).thenCallRealMethod();

            register.readConfig(Sets.newHashSet("key1", "key2"));

            verify(cache1).addListener(listener1.capture());
            verify(cache2).addListener(listener2.capture());

            listener1.getValue()
                    .notify(ImmutableMap.of("key1", ImmutableValue.builder()
                            .createIndex(0)
                            .modifyIndex(0)
                            .lockIndex(0)
                            .key("key1")
                            .flags(0)
                            .value(BaseEncoding.base64().encode("val1".getBytes()))
                            .build()));
            listener2.getValue()
                    .notify(ImmutableMap.of("key2", ImmutableValue.builder()
                            .createIndex(0)
                            .modifyIndex(0)
                            .lockIndex(0)
                            .key("key2")
                            .flags(0)
                            .value(BaseEncoding.base64().encode("val2".getBytes()))
                            .build()));

            assertEquals(2, configItemKeyedByName.size());
            assertEquals("val1", configItemKeyedByName.get("key1").get());
            assertEquals("val2", configItemKeyedByName.get("key2").get());
        }
    }