Refactoring Metadata Unit Tests

[heliang666s]

What is the purpose of the change?

Refactoring Metadata Unit Tests

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Make sure gitHub actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.82%. Comparing base (bc729af) to head (cb91ad9).

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #15089      +/-   ##
============================================
- Coverage     58.83%   58.82%   -0.01%     
  Complexity       12       12              
============================================
  Files          1883     1883              
  Lines         86013    86013              
  Branches      12886    12886              
============================================
- Hits          50602    50601       -1     
- Misses        29881    29884       +3     
+ Partials       5530     5528       -2     

Flag	Coverage Δ
unit-tests	58.82% <ø> (-0.01%)	⬇️

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[CrazyHZM]

Now that we've mocked ZookeeperClient, I think we can simulate the return result directly without actually storing it and spread the setUp logic across each unit test.