test: add biome selector regression coverage

[MichaelFisher1997]

Summary

• Add baseline regression coverage for biome selector outputs across ocean, coast, frozen ocean, lowland, mountain, hot/dry, cold, wet, and transition-prone inputs.
• Lock river and frozen river override priority plus height, slope, continentalness, ridge-mask baseline, and fallback behavior.

Verification

• nix develop --command zig fmt modules/world-worldgen/src/biome_selector_tests.zig
• nix develop --command zig build test

Fixes #648

[github-actions]

📋 Summary

This PR fixes #648 by adding regression test coverage for the biome selector system. It introduces 5 new tests covering climate/structural baseline selections, river/frozen-river priority overrides, structural constraint edge cases, ridge mask behavior, and Voronoi fallback logic. The implementation is test-only (no production code changes) and the test file is already registered in src/tests.zig:61.

📌 Review Metadata

• Reviewed Commit SHA: 00ff405c14359d5f807ac7a48443c0932ee9a2dd
• Reviewed PR: test: add biome selector regression coverage #664
• Linked Issues: Worldgen Phase 0: add biome selector regression tests #648 — Verified: The tests lock the baseline biome selector outputs described in the PR summary, covering ocean, coast, frozen ocean, lowland, mountain, hot/dry, cold, wet, and transition-prone inputs, plus river override and fallback behavior.

Overall quality is high: the tests are deterministic, pure (no allocators/GPU/window required), call real production functions, and expectations were manually verified against the BIOME_POINTS registry in biome_registry.zig.

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🔴 Critical Issues (Must Fix - Blocks Merge)

None identified.

⚠️ High Priority Issues (Should Fix)

None identified.

💡 Medium Priority Issues (Nice to Fix)

None identified.

ℹ️ Low Priority Suggestions (Optional)

[LOW] modules/world-worldgen/src/biome_selector_tests.zig:393 — Ridge mask test documents unused parameter
Confidence: High
Description: The test selectBiomeWithConstraints documents ridge mask baseline behavior passes ridge_mask: 0.0 and ridge_mask: 1.0 to selectBiomeWithConstraints, but that function only forwards height, continentalness, and slope to selectBiomeVoronoi — ridge_mask is silently ignored. The test therefore documents that ridge_mask has no effect, rather than testing any ridge mask logic.
Impact: If ridge mask logic is added later, this test will fail and need updating. It may mislead readers into thinking ridge_mask is already wired up.
Suggested Fix: Either add a comment inside the test body explaining that ridge_mask is currently unused by selectBiomeWithConstraints, or rename the test to "selectBiomeWithConstraints ignores ridge_mask (currently unused)" to make the intent explicit.

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📊 SOLID Principles Score

Principle	Score	Notes
Single Responsibility	9	Each test has one clear focus; the parameterized test uses a table but still verifies one concept.
Open/Closed	10	Pure test addition; no production code modified.
Liskov Substitution	N/A	Not applicable to test files.
Interface Segregation	9	Tests target specific functions (selectBiomeWithConstraints, selectBiomeVoronoi, etc.) without overloading.
Dependency Inversion	8	Tests call production functions directly; no mocks needed for pure logic.
Average	9.0

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🎯 Final Assessment

Overall Confidence Score: 92%

Confidence Breakdown:

• Code Quality: 95% (Clean, idiomatic Zig; follows existing conventions; good use of errdefer for debugging.)
• Completeness: 90% (Covers the stated requirements from Worldgen Phase 0: add biome selector regression tests #648. Could be stronger with non-exact-match Voronoi distances, but exact-match regression tests are valid.)
• Risk Level: 95% (Test-only change; zero runtime risk.)
• Test Coverage: 90% (5 focused tests; all deterministic and pure. Minor gap: ridge_mask is not actually exercised, only documented as ignored.)

Merge Readiness:

• All critical issues resolved
• SOLID average score >= 6.0
• Overall confidence >= 60%
• No security concerns
• Tests present and passing (if applicable)

Verdict:

MERGE

Clean test-only PR that locks biome selector baseline behavior. The one low-priority note about ridge_mask documentation is not blocking.

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  "reviewed_sha": "00ff405c14359d5f807ac7a48443c0932ee9a2dd",
  "critical_issues": 0,
  "high_priority_issues": 0,
  "medium_priority_issues": 0,
  "overall_confidence_score": 92,
  "recommendation": "MERGE"
}

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