More tests to increase code coverage for diskann

[JordanMaples]

This is in service of #927.

I was discussing the above issue with @hildebrandmw and he pointed out that one of the problems we have with code coverage is that there is a delta in reported coverage between runs where only diskann is specified and runs where diskann and diskann-providers is specified.

I ran the code coverage tool locally to identify some of these deltas and added a couple tests to gain coverage for index.rs.

[Copilot]

Pull request overview

Adds additional unit tests in diskann’s graph test suite to increase coverage in graph/index.rs and related deletion/consolidation paths, helping reduce coverage deltas vs. runs that include diskann-providers.

Changes:

• Adds new cases/index.rs tests covering QueryLabelProvider::on_visit default behavior and DiskANNIndex::count_reachable_nodes.
• Expands inplace-delete test coverage across multiple InplaceDeleteMethod variants with post-delete graph validation.
• Introduces shared 2D-square graph fixtures in cases/helpers.rs and adds consolidation tests for multiple ConsolidateKind outcomes.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
diskann/src/graph/test/cases/mod.rs	Registers new test modules (helpers, index).
diskann/src/graph/test/cases/helpers.rs	Adds shared 2D-square index/graph setup helpers used by multiple test cases.
diskann/src/graph/test/cases/index.rs	Adds tests targeting graph/index.rs code paths (QueryLabelProvider, count_reachable_nodes).
diskann/src/graph/test/cases/inplace_delete.rs	Adds tests for additional inplace-delete methods and validates resulting neighbor structure.
diskann/src/graph/test/cases/consolidate.rs	Extends consolidation test coverage for deleted/no-op/repair cases and transient failures.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.46193% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.47%. Comparing base (a90deb4) to head (1304820).

Files with missing lines	Patch %	Lines
diskann/src/graph/test/cases/inplace_delete.rs	94.47%	11 Missing ⚠️
diskann/src/graph/test/cases/index.rs	98.72%	5 Missing ⚠️
diskann/src/graph/test/cases/consolidate.rs	96.96%	2 Missing ⚠️
diskann/src/graph/test/cases/helpers.rs	97.72%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #953      +/-   ##
==========================================
+ Coverage   89.34%   89.47%   +0.12%     
==========================================
  Files         447      449       +2     
  Lines       83250    84038     +788     
==========================================
+ Hits        74378    75191     +813     
+ Misses       8872     8847      -25     

Flag	Coverage Δ
miri	89.47% <97.46%> (+0.12%)	⬆️
unittests	89.31% <97.46%> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann/src/graph/test/provider.rs	94.40% <100.00%> (+3.64%)	⬆️
diskann/src/graph/test/synthetic.rs	100.00% <100.00%> (ø)
diskann/src/graph/test/cases/consolidate.rs	97.65% <96.96%> (-0.74%)	⬇️
diskann/src/graph/test/cases/helpers.rs	97.72% <97.72%> (ø)
diskann/src/graph/test/cases/index.rs	98.72% <98.72%> (ø)
diskann/src/graph/test/cases/inplace_delete.rs	95.76% <94.47%> (-4.24%)	⬇️

... and 4 files with indirect coverage changes

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