protected List<ProviderInfo> resolveDomain(String directUrl) {
        List<ProviderInfo> providerInfos = domainCache.get(directUrl);
        if (providerInfos != null) {
            return providerInfos;
        }
        ProviderInfo providerInfo = convertToProviderInfo(directUrl);
        List<ProviderInfo> result = directUrl2IpUrl(providerInfo, domainCache.get(directUrl));
        domainCache.put(directUrl, result);
        return result;
    }
@Test
    public void testResolveDomain() {
        String mockKey = "mock";
        List<ProviderInfo> value = new ArrayList<>();
        domainRegistry.domainCache.put(mockKey, value);
        assertSame(value, domainRegistry.resolveDomain(mockKey));

        String local = "127.0.0.1";
        List<ProviderInfo> actual = domainRegistry.resolveDomain(local);
        assertEquals(1, actual.size());
        assertEquals(local, actual.get(0).getHost());
    }