code: func (c *testCluster) AddAgent() error {
  	// first node
  	if len(c.nodes) == 0 {
  		return fmt.Errorf("there is no manager nodes")
  	}
  	joinAddr, err := c.RandomManager().node.RemoteAPIAddr()
  	if err != nil {
  		return err
  	}
  	clusterInfo, err := c.GetClusterInfo()
  	if err != nil {
  		return err
  	}
  	node, err := newTestNode(joinAddr, clusterInfo.RootCA.JoinTokens.Worker, false, c.fips)
  	if err != nil {
  		return err
  	}
  	return c.AddNode(node)
  }
docs: // AddAgent adds node with Agent role(doesn't participate in raft cluster).