public static MockAddressResolverGroup always(String ip) {
        requireNonNull(ip, "ip");
        checkArgument(NetUtil.isValidIpV4Address(ip) || NetUtil.isValidIpV6Address(ip),
                      "not an IP address: %s", ip);
        try {
            final InetAddress resolved = InetAddress.getByName(ip);
            return new MockAddressResolverGroup(unused -> resolved);
        } catch (UnknownHostException e) {
            throw new IllegalArgumentException(e);
        }
    }
Creates an {@link AddressResolverGroup} which always returns the specified {@code ip} address
for any hostname.
testing-internal/src/main/java/com/linecorp/armeria/internal/testing/MockAddressResolverGroup.java