Added unit tests for the mock EstimatorClient

[anujagrawal699]

Description:
This PR adds unit tests for the mock EstimatorClient, which is used for testing the scheduler estimator service functionality in Karmada. The tests ensure proper behavior of both success and error scenarios for unschedulable replicas calculation and maximum available replicas estimation.

Additions:

1. pkg/estimator/service/mock_EstimatorClient_test.go

Test Coverage:

1. pkg/estimator/service/mock_EstimatorClient.go : 0% to 82.40%

What type of PR is this?
/kind feature

Which issue(s) this PR fixes:
Fixes a part of #5470

Does this PR introduce a user-facing change?:

NONE

[karmada-bot]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.35%. Comparing base (6f4d69c) to head (2532dfe).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5894      +/-   ##
==========================================
+ Coverage   46.32%   46.35%   +0.02%     
==========================================
  Files         663      663              
  Lines       54756    54756              
==========================================
+ Hits        25367    25383      +16     
+ Misses      27761    27739      -22     
- Partials     1628     1634       +6     

Flag	Coverage Δ
unittests	46.35% <ø> (+0.02%)	⬆️

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[XiShanYongYe-Chang]

/retest
/assign

[XiShanYongYe-Chang]

I have a question, the MockEstimatorClient itself is already prepared for testing, do we still need to test the tests?

[anujagrawal699]

I have a question, the MockEstimatorClient itself is already prepared for testing, do we still need to test the tests?

Yeah you're right, i was following the path of increasing test coverage. But it is not good to write tests just for coverage numbers.
I think we should move ahead without this PR.

[XiShanYongYe-Chang]

i was following the path of increasing test coverage.

We should have code maintainability as the first element. :)