@VisibleForTesting
    ServingStatus checkServingStatus(String serviceName) {
        if (!isServerHealthy()) {
            return ServingStatus.NOT_SERVING;
        }
        if (Strings.isNullOrEmpty(serviceName)) {
            return ServingStatus.SERVING;
        }
        final ListenableHealthChecker listenableHealthChecker = grpcServiceHealthCheckers.get(serviceName);
        if (listenableHealthChecker == null) {
            return ServingStatus.SERVICE_UNKNOWN;
        }
        if (listenableHealthChecker.isHealthy()) {
            return ServingStatus.SERVING;
        }
        return ServingStatus.NOT_SERVING;
    }
Returns a new builder which builds a new {@link GrpcHealthCheckService}.
grpc/src/main/java/com/linecorp/armeria/server/grpc/GrpcHealthCheckService.java