code: private Set<String> validateJobHealthCheck(final Job job) {
      final HealthCheck healthCheck = job.getHealthCheck();
  
      if (healthCheck == null) {
        return emptySet();
      }
  
      final Set<String> errors = Sets.newHashSet();
  
      if (healthCheck instanceof ExecHealthCheck) {
        final List<String> command = ((ExecHealthCheck) healthCheck).getCommand();
        if (command == null || command.isEmpty()) {
          errors.add("A command must be defined for `docker exec`-based health checks.");
        }
      } else if (healthCheck instanceof HttpHealthCheck || healthCheck instanceof TcpHealthCheck) {
        final String port;
        if (healthCheck instanceof HttpHealthCheck) {
          port = ((HttpHealthCheck) healthCheck).getPort();
        } else {
          port = ((TcpHealthCheck) healthCheck).getPort();
        }
  
        final Map<String, PortMapping> ports = job.getPorts();
        if (isNullOrEmpty(port)) {
          errors.add("A port must be defined for HTTP and TCP health checks.");
        } else if (!ports.containsKey(port)) {
          errors.add(format("Health check port '%s' not defined in the job. Known ports are '%s'",
              port, Joiner.on(", ").join(ports.keySet())));
        }
      }
  
      return errors;
    }
docs: Validate the Job's health check.
  
  @param job The Job to check.
  
  @return A set of error Strings