refactor: use struct embedding to avoid interface forwarding

[CodeBear801]

issue: #279

• Use struct embedding to avoid function calling to interface implemented in base class
  • https://golang.org/doc/effective_go.html#embedding
  • https://github.com/wangyoucao577/golang/tree/master/effective-go#embedding
  • https://play.golang.org/p/F6gmScefu5s
  • https://play.golang.org/p/xekNSmRLk9H
• Remove unnecessary go-routine in test
• Adjust name

Tasklist

• refactor
• review