code: func (c *testCluster) RandomManager() *testNode {
  	var managers []*testNode
  	for _, n := range c.nodes {
  		if n.IsManager() {
  			managers = append(managers, n)
  		}
  	}
  	idx := rand.Intn(len(managers))
  	return managers[idx]
  }
docs: // RandomManager chooses random manager from cluster.