Improve test coverage for /pkg/controllers/binding

[xovoxy]

What type of PR is this?
/kind failing-test

What this PR does / why we need it:
Improved test coverage for /pkg/controllers/binding from 36.4% to 64.9%
Which issue(s) this PR fixes:
Part: #5235

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.72%. Comparing base (37488bd) to head (effcc6c).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5342      +/-   ##
==========================================
+ Coverage   28.53%   28.72%   +0.18%     
==========================================
  Files         632      632              
  Lines       43856    43856              
==========================================
+ Hits        12515    12596      +81     
+ Misses      30443    30353      -90     
- Partials      898      907       +9     

Flag	Coverage Δ
unittests	28.72% <ø> (+0.18%)	⬆️

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[XiShanYongYe-Chang]

Thanks~
/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: XiShanYongYe-Chang

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• pkg/controllers/OWNERS [XiShanYongYe-Chang]

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