[WIP] Test for etcd metrics

[dims]

The test being added here will fail until #19195 lands

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @dims. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.72%. Comparing base (7c56ef2) to head (f55b375).

Additional details and impacted files

see 49 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19242      +/-   ##
==========================================
- Coverage   68.77%   67.72%   -1.05%     
==========================================
  Files         420      420              
  Lines       35649    35649              
==========================================
- Hits        24518    24145     -373     
- Misses       9705    10075     +370     
- Partials     1426     1429       +3     

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[serathius]

Can we first merge the test?