??????Optimize shenyu-plugin-base module unit test

[boush-face]

issue: https://github.com/dromara/shenyu/issues/1449#issue-890919183


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??????:                                                                         
                                               "boush-face"                     
                                                               
<978226...@qq.com&gt;;
????????:&nbsp;2021??5??13??(??????) ????6:33
??????:&nbsp;"dev"<dev@shenyu.apache.org&gt;;

????:&nbsp;Optimize shenyu-plugin-base module unit test




Task

Task List:

Optimize shenyu-plugin-base module unit test??make its coverage rate is more 
than 80%