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 60.75%. Comparing base (628dcbf) to head (63980a4).

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #15089      +/-   ##
============================================
- Coverage     60.76%   60.75%   -0.02%     
- Complexity    10863    10864       +1     
============================================
  Files          1882     1882              
  Lines         86007    86007              
  Branches      12886    12886              
============================================
- Hits          52263    52253      -10     
- Misses        28301    28308       +7     
- Partials       5443     5446       +3     

Flag	Coverage Δ
integration-tests	33.13% <ø> (+0.15%)	⬆️
samples-tests	29.21% <ø> (-0.01%)	⬇️
unit-tests	58.91% <ø> (-0.02%)	⬇️

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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.