code: func (d *Daemon) CheckActiveContainerCount(c *check.C) (interface{}, check.CommentInterface) {
  	out, err := d.Cmd("ps", "-q")
  	assert.NilError(c, err)
  	if len(strings.TrimSpace(out)) == 0 {
  		return 0, nil
  	}
  	return len(strings.Split(strings.TrimSpace(out), "\n")), check.Commentf("output: %q", string(out))
  }
docs: // CheckActiveContainerCount returns the number of active containers
  // FIXME(vdemeester) should re-use ActivateContainers in some way