fix(throttler/demo): rename underscore flags to dash format, add manager tests

[ManthanNimodiya]

Description

Three flag names in the throttler demo binary (lag_update_interval, replica_degration_interval, replica_degration_duration) still used underscore separators, conflicting with the project-wide standard established in v25. This PR renames them and migrates all flag registrations in registerDemoFlags to utils.SetFlag* wrappers to match the pattern used across every other Vitess binary.

Also adds TestManager_Throttlers and TestManager_Log to manager_test.go — both methods existed without any dedicated test coverage.

Related Issue(s)

Fixes part of #17880 (flag renaming: replace underscores with dashes)
Related to #14931 (improve unit test coverage)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

No deployment impact. The throttler demo is a local diagnostic binary, not a production component. The flag rename is intentional — v25 removes underscore flag support.

AI Disclosure

Issue scope was analysed thoroughly before implementing this fix.

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

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• Ensure that the Pull Request has a descriptive title.
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Backward compatibility

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• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
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[Copilot]

Pull request overview

This PR aligns the throttler demo binary with Vitess’ dash-separated flag naming standard for v25 and adds direct unit coverage for two manager helper methods in the throttler package.

Changes:

• Renames the throttler demo’s remaining underscore-separated flags to dash-separated forms.
• Switches registerDemoFlags to the shared utils.SetFlag* registration helpers used elsewhere in the codebase.
• Adds unit tests for Manager.Throttlers() and managerImpl.log().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
go/vt/throttler/manager_test.go	Adds focused tests for throttler name listing and log lookup error handling.
go/vt/throttler/demo/throttler_demo.go	Renames demo CLI flags and uses the shared flag registration wrappers.

[ManthanNimodiya]

@mattlord - please have a review when you get chance

[ManthanNimodiya]

@mattlord - removed the entire demo directory as suggested, please have a review when you get chance

[mattlord]

LGTM. Thank you, @ManthanNimodiya ! But let's please not open new PRs that offer/cover so little. It adds load to the shared CI systems and the maintainers. The Manager stuff was not even something listed in the noted issue and I don't see much practical value in these unit tests TBH.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.22%. Comparing base (70c7a72) to head (75afe77).
⚠️ Report is 255 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20033      +/-   ##
==========================================
+ Coverage   69.67%   72.22%   +2.55%     
==========================================
  Files        1614     1346     -268     
  Lines      216793   204634   -12159     
==========================================
- Hits       151044   147794    -3250     
+ Misses      65749    56840    -8909     

Flag	Coverage Δ
partial	72.22% <ø> (?)

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[mattlord]

@ManthanNimodiya And the DCO test is failing... I'm almost ready to close this as the review and CI overhead is IMO too much for a trivial change. But since we are already here, I will keep on with this one.

[ManthanNimodiya]

@mattlord, sorry for the extra noise on CI and your time.
I'll make sure future PRs are more focused and scoped to what's actually needed.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

go/vt/throttler/demo/throttler_demo.go:1

• The PR description says this demo should keep existing functionality while renaming three flags, but this change deletes the entire throttler demo package. After the deletion, go/vt/throttler/demo no longer exists, so the local diagnostic binary and all of its behavior are removed rather than migrated to dash-form flag names.