Fix regression & Improve test coverage related to 'DijkstraMap'

[ChrisLee02]

What

Restore Dijkstra start tiles as seeded distance values and add regression coverage for the restored behavior.

Why

DijkstraMap.map is public distance data, but the current build paths only write neighboring tiles during expansion. That leaves start tiles with a return-path cost instead of the expected seed distance, which can affect direct map reads and helper-based path selection.

This PR restores the intended seed behavior for build, build_weighted, and threaded build_parallel, then locks the behavior with tests for constructor output, weighted starts, empty maps, clearing, and lowest-exit selection.

Closes #26

Checklist

Required

• cargo check --all passes
• cargo fmt --all -- --check passes
• cargo clippy --workspace --all-targets -- -D warnings -A clippy::multiple-crate-versions passes
• cargo test --all passes
• I linked the related issue

Threaded Dijkstra path was verified separately with cargo test -p bracket-pathfinding --features threaded dijkstra::test -- --nocapture

Functional Validation

• Behavior related to this change was verified locally (if applicable)
• Rendering/backend behavior was verified when runtime code changed (if applicable)
• Algorithm behavior (pathfinding/FOV/noise/random) was verified when affected (if applicable)
• I added or updated tests for changed behavior (if applicable)

Configuration & Docs

• User-facing docs were updated (README.md, ARCHITECTURE.md, or relevant manual pages, if applicable)
• New dependencies/configuration are documented (if applicable)
• No sensitive values or credentials were introduced

If Applicable

• Security impact considered (run cargo audit locally if needed)
• Breaking behavior changes are clearly described in this PR

Summary by CodeRabbit

• Bug Fixes
  • Improved pathfinding algorithm reliability through corrected initialization of distance calculations at starting positions, ensuring more accurate navigation results in pathfinding operations.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR updates Dijkstra pathfinding initialization to explicitly set start tile distances before propagation and adds comprehensive unit test coverage. Unweighted and weighted builds now initialize distances with min(current, 0.0) and min(current, start_weight) respectively, applied across all three build methods. Five new unit tests validate initialization, clearing, and pathfinding correctness.

Changes

Start tile initialization and test coverage

Layer / File(s)	Summary
Start tile distance initialization bracket-pathfinding/src/dijkstra.rs	build, build_weighted, and parallel build now initialize dm.map at each start index using min(current, 0.0) or min(current, start_weight) before enqueueing, ensuring correct per-start distances prior to open list propagation.
Test module and unit test coverage bracket-pathfinding/src/dijkstra.rs	Test module diagram updated; new unit tests test_new, test_new_weighted, test_new_empty, test_clear, and test_lowest_exit assert expected depth arrays, verify f32::MAX initialization and reset behavior, and confirm pathfinding choices from specific positions.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

A rabbit hops through paths so true,
Start tiles now know their way anew—
With zero distance, weights in place,
Tests sprint ahead with steady grace! 🐰✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: fixing a regression in DijkstraMap initialization and adding comprehensive test coverage to prevent future regressions.
Linked Issues check	✅ Passed	The PR directly addresses issue #26 by adding multiple test cases (test_new, test_new_weighted, test_new_empty, test_clear, test_lowest_exit) to strengthen test coverage and validate DijkstraMap behavior.
Out of Scope Changes check	✅ Passed	All changes are within scope: regression fix for DijkstraMap seeding behavior and test additions directly support the stated objectives of fixing the bug and improving test coverage.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@bracket-pathfinding/src/dijkstra.rs`:
- Around line 355-407: Add a threaded-only unit test that exercises
DijkstraMap::build_parallel by supplying at least THREADED_REQUIRED_STARTS (>=4)
start positions; create a new #[test] function annotated with #[cfg(feature =
"threaded")] (e.g., fn test_new_threaded()) in the same tests module, construct
a MiniMap, call DijkstraMap::new (or new_weighted) with 4+ start indices, and
assert the resulting map contents or properties match expected values so the
parallel code path (DijkstraMap::build_parallel) is exercised and validated.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 0c27ed64-bd1b-4929-bbce-be1b39669f0b

📥 Commits

Reviewing files that changed from the base of the PR and between 5612251 and e6756de.

📒 Files selected for processing (1)

• bracket-pathfinding/src/dijkstra.rs

📜 Review details

🧰 Additional context used

📓 Path-based instructions (1)

**/*.rs

📄 CodeRabbit inference engine (AGENTS.md)

**/*.rs: Format all Rust code using cargo fmt --all
Fix all cargo clippy warnings — the CI enforces -D warnings
Add tests for new functionality in the relevant module; for split domains, prefer colocated tests.rs

Files:

• bracket-pathfinding/src/dijkstra.rs

🔇 Additional comments (1)

bracket-pathfinding/src/dijkstra.rs (1)

151-153: LGTM!

Also applies to: 183-185, 230-232

[utilForever]

LGTM. Thanks for your work! 🧪