introduce tests to check whether workqueue metrics exist

[chaosi-zju]

What type of PR is this?

/kind failing-test

What this PR does / why we need it:

introduce tests to check whether workqueue metrics exist

Which issue(s) this PR fixes:

Fixes part of #5954

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.39%. Comparing base (ba1e68d) to head (bed16d1).
Report is 7 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6003      +/-   ##
==========================================
+ Coverage   48.37%   48.39%   +0.02%     
==========================================
  Files         665      665              
  Lines       54795    54811      +16     
==========================================
+ Hits        26507    26527      +20     
+ Misses      26569    26567       -2     
+ Partials     1719     1717       -2     

Flag	Coverage Δ
unittests	48.39% <ø> (+0.02%)	⬆️

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