test: add some UT for server module

[WangzJi]

• I have read the CONTRIBUTING.md guidelines.
• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.75%. Comparing base (61e375f) to head (64e7f7d).

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #7750      +/-   ##
============================================
+ Coverage     66.17%   66.75%   +0.58%     
+ Complexity      994      992       -2     
============================================
  Files          1323     1323              
  Lines         50155    50155              
  Branches       5928     5928              
============================================
+ Hits          33190    33483     +293     
+ Misses        14053    13758     -295     
- Partials       2912     2914       +2     

see 36 files with indirect coverage changes

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