test(locked_outpoints): add unit tests for ChangeSet merge and is_empty

[KrishnaShuk]

Description

This PR adds unit test coverage for locked_outpoints::ChangeSet, which previously had zero inline tests. It tests the Merge trait implementations, ensuring that merge() and is_empty() behave correctly under various conditions.

Notes to the reviewers

• Added 6 deterministic tests verifying:
  • Default initialization is empty
  • Merging with empty datasets are clean no-ops
  • Disjoint changeset merges successfully combine outpoints
  • Overwriting logic accurately fulfills the extend() semantics where the incoming other duplicate outpoints overwrite self
• Uses idiomatic boolean assertions (assert!(...)) verified cleanly by cargo clippy.
• Tests use Txid::from_byte_array internally to maintain deterministic speed without relying on rand.

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.25%. Comparing base (826b19f) to head (6c15a6c).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #436      +/-   ##
==========================================
+ Coverage   80.04%   80.25%   +0.21%     
==========================================
  Files          24       24              
  Lines        5336     5393      +57     
  Branches      242      242              
==========================================
+ Hits         4271     4328      +57     
  Misses        987      987              
  Partials       78       78              

Flag	Coverage Δ
rust	80.25% <100.00%> (+0.21%)	⬆️

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[lambaaryan011]

Issues Found

1. Missing Test for Multiple Merges

   • The code only tests 2 merges (true → false)
   • Should test 3+ merges (true → false → true → false)
   • Example: What if merge happens 10 times?

2. Missing Implementation Code

   • Tests check merge() but we can't see merge() code
   • Need to see the actual implementation
   • Can't verify tests are correct without it

3. Unclear Checklist

   • "breaks the existing API" is confusing
   • Does it break or not? Need clarity

Good Things

• Tests are written correctly
• Uses assert!() properly
• Deterministic (no random data)

[luisschwab]

@lambaaryan011 you only waste everyone's time with this LLM review.

[lambaaryan011]

@luisschwab That’s fair — my earlier comment wasn’t very useful.

I’ll take a closer look at the implementation and follow up with more concrete feedback.