@Override
    public Optional<RawConfig> getConfig(RawConfig input, JRTServerConfigRequest request) {
        RawConfig config = getConfig(input.getKey());
        memoryCache.update(config);
        return Optional.of(config);
    }
Mock client that always returns with config immediately

@author hmusum
config-proxy/src/test/java/com/yahoo/vespa/config/proxy/MockConfigSourceClient.java