[draft]add test for limiter

[nolouch]

What problem does this PR solve?

Issue Number: Close #xxx

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456, multiple issues should use full syntax for each issue and be separated by a comma, like: Issue Number: close #123, ref #456.

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[ti-chi-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.33%. Comparing base (ca179e6) to head (ab64f11).
Report is 20 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8434      +/-   ##
==========================================
+ Coverage   77.24%   77.33%   +0.08%     
==========================================
  Files         471      471              
  Lines       61696    61922     +226     
==========================================
+ Hits        47660    47890     +230     
+ Misses      10454    10442      -12     
- Partials     3582     3590       +8     

Flag	Coverage Δ
unittests	77.33% <ø> (+0.08%)	⬆️

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