MyBatis [tests] Improve test coverage.

There is no implement method selectPostsById() , in the Test module BoundBlogMapper interface class ,I implemented that method, Improve test coverage.

Comment From: kazuki43zoo

@yangfancoming Thanks for your contributing!

Could your indicate covered line or covered condition using http://www.mybatis.org/mybatis-3/jacoco/index.html by this changes?

Comment From: yangfancoming

@yangfancoming Thanks for your contributing!

Could your indicate covered line or covered condition using http://www.mybatis.org/mybatis-3/jacoco/index.html by this changes?

Sorry ，I haven't used jacoco, and I will going to study it. Thanks~

Comment From: yangfancoming