tests: increase coverage for multiple files in vitess/go/stats to 100%

[EshaanAgg]

Description

Added 100% test coverage for the following files:

• vitess/go/stats/histogram
• vitess/go/stats/hooks
• vitess/go/stats/ring
• vitess/go/stats/snake_case_converter

Also refactored some of the existing tests to use the assert library for cleaner tests, and added a function called AddHook on the Histogram struct so that the users can register a hook on the histogram which can be called anytime a value is added to the same (this seemed to be the desired functionality according to the existing code, but the registration of the hook seems to be omitted)

Related Issue(s)

Fixes part of #14931

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

[vitess-bot]

Review Checklist

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

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9af8692) 47.33% compared to head (bde4f2c) 47.35%.
Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14997      +/-   ##
==========================================
+ Coverage   47.33%   47.35%   +0.02%     
==========================================
  Files        1142     1142              
  Lines      239009   239020      +11     
==========================================
+ Hits       113125   113183      +58     
+ Misses     117289   117242      -47     
  Partials     8595     8595              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[frouioui]

Looks good to me, thank you!