Add unit tests to nacos 2.0

[realJackSun]

Issue Description

Now the unit test coverage rate of nacos 2.0 is too low, could you add more unit tests?

Anything else we need to know?

To-do list:

• Add unit tests for module nacos-client Add unit tests to nacos-client module in nacos2.0 #5011
• Add unit tests for module nacos-config Add unit tests for module nacos-config in nacos 2.0 #5092
• Add unit tests for module nacos-consistency Add unit tests for module nacos-consistency in nacos 2.0 #5093
• Add unit tests for module nacos-core Add unit tests for module nacos-core in nacos 2.0 #5094
• Add unit tests for module nacos-common Add unit tests for module nacos-common in nacos 2.0 #5095
• Add unit tests for module nacos-naming Add unit tests to nacos-naming module in nacos2.0 #4982

[shalk]

Add unit tests for module nacos-client repeat twice.

I think i can add some ut for nacos-client , so i create #5011

[realJackSun]

该ISSUE为nacos2.0单元测试模块的根ISSUE，为nacos2.0各个模块的单测开发ISSUE提供总索引。

[SunJiFengPlus]

Is there any define of done? for example, the (class/line/branch) coverage reaches 60%.

[Salhazry]

Issue Description

Now the unit test coverage rate of nacos 2.0 is too low, could you add more unit tests?

Anything else we need to know?

To-do list:

• Add unit tests for module nacos-client Add unit tests to nacos-client module in nacos2.0 #5011
• Add unit tests for module nacos-config Add unit tests for module nacos-config in nacos 2.0 #5092
• Add unit tests for module nacos-consistency Add unit tests for module nacos-consistency in nacos 2.0 #5093
• Add unit tests for module nacos-core Add unit tests for module nacos-core in nacos 2.0 #5094
• Add unit tests for module nacos-common Add unit tests for module nacos-common in nacos 2.0 #5095
• Add unit tests for module nacos-naming Add unit tests to nacos-naming module in nacos2.0 #4982