Test Suite Review for Boost Submission¶
Review Date: 2025-10-22 Reviewer: TDD Architecture Analysis Status: 36 tests passing, 216 assertions
Executive Summary¶
The test suite is well-structured with good coverage of core functionality, but has critical gaps that must be addressed before Boost submission. The Boost review process is rigorous and will specifically look for edge cases, exception safety guarantees, and thorough verification of documented behavior.
Overall Grade: B+ (Good foundation, needs refinement)
Test Organization Analysis¶
Strengths¶
- Clear separation of concerns across 7 test files
- Good use of BDD-style Given-When-Then in correctness tests
- Appropriate test granularity - unit tests focused on single behaviors
- STL compatibility verified with multiple container types
- Performance characteristics validated (10K entity stress tests)
- Multi-dimensional support tested (2D, 3D, 4D)
Current Coverage¶
test_basic.cpp - Core operations (construction, rebuild, update, queries)
test_topology.cpp - Topology behaviors (bounded, toroidal, infinite)
test_queries.cpp - Query operations and iteration
test_correctness.cpp - Algorithmic correctness (Morton, pairs, incremental)
test_types_and_precision.cpp - Type system, precision, large-scale
test_advanced.cpp - STL compat, move/copy semantics, statistics
test_edge_cases.cpp - Recently added edge cases
CRITICAL GAPS FOR BOOST SUBMISSION¶
1. Exception Safety Verification (HIGH PRIORITY)¶
The header documents exception safety guarantees but no tests verify them:
Documented Guarantees: - Queries: Nothrow guarantee - Single-entity operations: Strong guarantee - Bulk operations: Basic guarantee
Missing Tests:
// MUST ADD: Test that queries don't throw
TEST_CASE("Query operations provide nothrow guarantee") {
// Verify query_radius, for_each_pair, cell_entities never throw
// Even with invalid inputs (negative radius, out-of-bounds coords)
}
// MUST ADD: Test exception safety during rebuild
TEST_CASE("rebuild provides basic guarantee on exception") {
// If allocation fails mid-rebuild, grid should be in valid state
// (possibly empty, but not corrupted)
}
// MUST ADD: Test strong guarantee for single operations
TEST_CASE("reserve_entities provides strong guarantee") {
// If allocation fails, grid unchanged
}
Recommendation: Add test_exception_safety.cpp with tests for: - Out-of-memory scenarios (mock allocator) - Invalid position_accessor throws - Container iteration throws - Verify nothrow noexcept declarations
2. Morton Encoding Coordinate Limits (HIGH PRIORITY)¶
Header documents limits but only minimal testing:
Documented Limits (lines 180-186): - 2D: ±2^31 cells (~2 billion) - 3D: ±2^21 cells (~2 million) - 4D+: Further reduced range
Current Testing: - test_edge_cases.cpp has "Large coordinates in infinite topology" but uses ±10,000 (trivial) - No tests at actual limits (±2^21 for 3D, ±2^31 for 2D) - No tests for hash collision behavior at limit boundaries
Missing Critical Tests:
TEST_CASE("Morton encoding at documented 2D limits") {
// Cell coordinates exactly at ±2^31 should work
// Cell coordinates beyond ±2^31 should have hash collisions
// Verify documented behavior matches implementation
}
TEST_CASE("Morton encoding at documented 3D limits") {
// Test at ±2^21 (not ±10,000!)
// Verify hash collisions beyond limits are handled gracefully
}
TEST_CASE("3D infinite topology warns about coordinate limits") {
// Particles beyond ±2^21 cells should still work
// But document that performance degrades (hash collisions)
}
Why This Matters: Boost reviewers will ask "what happens at the documented limits?" Current tests don't answer this.
3. The Recent Fixes Lack Verification (HIGH PRIORITY)¶
You mentioned 4 recent fixes but only 1 has dedicated tests:
Fix 1: entity_count() auto-tracks on rebuild - ✅ Tested in test_edge_cases.cpp::entity_count after various operations - ✅ Tested in test_basic.cpp::Grid capacity methods
Fix 2: cell_entities() return type consistency - ✅ Tested in test_edge_cases.cpp::cell_entities() with unoccupied cells - ⚠️ But doesn't test type consistency (returns same view type for empty/occupied)
Fix 3: Morton encoding coordinate limits - ❌ NOT TESTED AT ACTUAL LIMITS (see section 2)
Fix 4: Overflow protection in constructor - ⚠️ Partially tested in test_edge_cases.cpp::Overflow protection in constructor - ❌ Only tests that it "doesn't crash" - doesn't verify the 1M cap - ❌ Doesn't test edge case: exactly 1M cells
Missing Verification:
TEST_CASE("Constructor overflow protection caps at 1M cells") {
// 1000³ = 1B cells, should cap reserve at 1M
grid_config<3> cfg{
.cell_size = {1.0f, 1.0f, 1.0f},
.world_size = {1000.0f, 1000.0f, 1000.0f},
.topology_type = topology::bounded
};
sparse_spatial_hash<Particle, 3> grid(cfg);
// Verify internal capacity is capped (needs friend or stats method)
// Or test indirectly: should not allocate 100MB+ on construction
}
TEST_CASE("cell_entities returns consistent view type") {
// Empty cell and occupied cell should return same range type
auto empty_view = grid.cell_entities(empty_cell);
auto occupied_view = grid.cell_entities(occupied_cell);
static_assert(std::same_as<decltype(empty_view), decltype(occupied_view)>);
}
4. Topology Edge Cases - Boundary Transitions (MEDIUM PRIORITY)¶
Current Testing: - Tests entities inside each topology - Tests entities far outside bounds - ❌ Missing: entities crossing boundaries during update
Missing Tests:
TEST_CASE("Bounded topology - entity crosses from in-bounds to out-of-bounds") {
// Start at (45, 45) - valid
// Move to (55, 55) - still valid
// Move to (105, 105) - should clamp
// Verify clamping happens correctly during update()
}
TEST_CASE("Toroidal topology - entity wraps around during update") {
// Start at (95, 95) - near edge
// Move to (105, 105) - should wrap to (5, 5)
// Verify wrap happens, old cell cleaned up
// Verify for_each_pair still finds pairs across wrap boundary
}
TEST_CASE("Topology change mid-simulation") {
// Build grid with bounded topology
// Rebuild with toroidal topology (same entities)
// Verify cell placement changes appropriately
}
5. Concurrent Access (MEDIUM PRIORITY - Document Only?)¶
Current State: - No tests for thread safety - No documentation about thread safety guarantees
For Boost Submission: You need to document thread safety (even if answer is "not thread-safe"):
/**
* Thread Safety: This class is NOT thread-safe.
* - Const methods (queries) are safe for concurrent reads
* - Modifying methods require external synchronization
* - rebuild()/update() invalidate all iterators
*/
Optional Tests (if you claim const methods are thread-safe):
TEST_CASE("Concurrent queries are safe") {
// Build grid once
// Multiple threads call query_radius simultaneously
// Verify no crashes, correct results
}
6. Iterator and Range Invalidation (MEDIUM PRIORITY)¶
Current Testing: - Tests that cells() and cell_contents() work - ❌ Doesn't test what invalidates them
Missing Tests:
TEST_CASE("Iterators invalidated by rebuild") {
grid.rebuild(particles);
auto cells_view = grid.cells();
auto it = cells_view.begin();
grid.rebuild(particles); // Invalidates iterators
// Document: using 'it' now is undefined behavior
// Can't easily test UB, but document it clearly
}
TEST_CASE("cell_entities view not invalidated by unrelated operations") {
grid.rebuild(particles);
auto cell_view = grid.cell_entities(some_cell);
grid.query_radius(...); // Should NOT invalidate
// Verify cell_view still usable
}
7. Type System Edge Cases (LOW-MEDIUM PRIORITY)¶
Current Testing: - Tests custom types with position_accessor - Tests double precision - ❌ Missing: what happens with wrong specialization?
Missing Tests:
TEST_CASE("position_accessor specialization mismatch detected") {
// Specialize for 2D but use 3D grid
// Should fail at compile time (concept enforcement)
// Document with static_assert examples
}
TEST_CASE("position_accessor returning inconsistent types") {
// One call returns float, next returns double
// Should compile but may lose precision
// Document expected behavior
}
TEST_CASE("Empty range handling") {
std::vector<Particle> empty;
grid.rebuild(empty);
// All operations should work with empty grid
REQUIRE(grid.empty());
REQUIRE(grid.stats().total_entities == 0);
auto results = grid.query_radius(100.0f, 0.0f, 0.0f, 0.0f);
REQUIRE(results.empty());
}
8. for_each_pair Correctness - More Scenarios (LOW PRIORITY)¶
Current Testing: - Tests no duplicates - Tests i < j ordering - Tests pair count for same-cell entities
Good Additional Coverage:
TEST_CASE("for_each_pair with zero radius") {
// Should only process entities in exactly same cell
// Not neighboring cells
}
TEST_CASE("for_each_pair callback throws") {
// What happens if callback throws mid-iteration?
// Document: basic exception guarantee (some pairs processed)
}
TEST_CASE("for_each_pair with exactly 1 entity") {
// Should call callback 0 times (no pairs)
}
TEST_CASE("for_each_pair skips empty cells efficiently") {
// Sparse grid (99% empty) should not iterate empty cells
// Verify performance doesn't degrade
}
9. Configuration Edge Cases (LOW PRIORITY)¶
Missing Tests:
TEST_CASE("Non-uniform world_size and cell_size") {
// cell_size = {1, 10, 100}
// world_size = {10, 100, 1000}
// Verify resolution calculation correct per dimension
}
TEST_CASE("Cell size larger than world size") {
// world_size = {10, 10}, cell_size = {100, 100}
// Results in 1x1 grid (all entities in one cell)
// Should work, just inefficient
}
TEST_CASE("Zero cell size (invalid config)") {
// Should this be undefined behavior?
// Or should constructor throw/assert?
// Document expected behavior
}
TEST_CASE("Negative cell size (invalid config)") {
// Same as above - document behavior
}
Test Quality Issues¶
1. Over-Conservative Assertions¶
Many tests use conservative checks that hide potential bugs:
// ❌ Current (too conservative)
REQUIRE(results.size() >= 1);
// ✅ Better (exact expectation)
REQUIRE(results.size() == 2); // Exactly particles 0 and 1
Files with this issue: - test_basic.cpp lines 129, 145, 226 - test_topology.cpp lines 112, 174 - test_queries.cpp lines 102, 256
Why it matters: Conservative assertions let bugs slip through. If you expect 2 results but get 10, test still passes.
Fix: Use exact counts where possible, or document why conservatism is needed:
// Conservative due to cell-based query returning all entities in cells
// within bounding box (may include entities outside actual radius)
REQUIRE(results.size() >= 2);
REQUIRE(results.size() <= 10); // But should not be wildly off
2. Magic Numbers Without Context¶
Fix: Add comments or constants:
// Use coprime multipliers to ensure pseudo-random distribution
constexpr int PRIME1 = 73;
constexpr int PRIME2 = 137;
constexpr int PRIME3 = 197;
3. Missing Failure Messages¶
Many tests lack informative failure messages:
// ❌ Current
REQUIRE(grid.cell_count() == 2);
// ✅ Better
REQUIRE(grid.cell_count() == 2,
"Expected 2 cells but got " << grid.cell_count());
Catch2 supports this - use INFO() or message arguments for complex checks.
Missing Documentation Verification¶
The header documents specific behaviors that should have tests:
From Header Line 255: "Memory: O(occupied_cells + entity_count)"¶
TEST_CASE("Memory scales with occupied cells, not total cells") {
// Create sparse grid (1% occupancy)
// Verify memory doesn't scale with total_cells
// This is tested in test_types_and_precision.cpp but could be clearer
}
From Header Line 487: "Measured speedup: ~40x"¶
TEST_CASE("update() is significantly faster than rebuild()") {
// Verify 10x+ speedup (40x may be optimistic)
// Current tests measure this but don't assert on ratio
}
From Header Line 621: "Skip already processed" (for_each_pair)¶
TEST_CASE("for_each_pair processes each pair exactly once") {
// Already tested in test_correctness.cpp
// But add explicit check that same pair never seen twice
}
Recommended New Test Files¶
test_exception_safety.cpp (CRITICAL)¶
- Nothrow guarantees for queries
- Basic guarantee for rebuild/update
- Strong guarantee for reserve_entities
- Out-of-memory scenarios
test_limits.cpp (CRITICAL)¶
- Morton encoding at documented limits (±2^31 for 2D, ±2^21 for 3D)
- Hash collision behavior
- Overflow protection verification
- Extreme coordinate values
test_documented_behavior.cpp (HIGH PRIORITY)¶
- Every complexity guarantee has a test
- Every exception safety claim verified
- All examples from README compile and work
- All edge cases mentioned in comments tested
Boost Review Preparation Checklist¶
Before Submission¶
- All exception safety guarantees verified with tests
- Morton encoding limits tested at actual documented values
- Recent fixes have dedicated regression tests
- Thread safety guarantees documented (even if "not thread-safe")
- Iterator invalidation rules documented and tested
- All conservative assertions reviewed and justified
- Magic numbers explained
- Failure messages provide debugging context
Nice-to-Have¶
- Benchmark tests prove documented performance claims
- Coverage report shows >90% line coverage
- Valgrind/sanitizer runs clean (no leaks, UB)
- All compiler warnings addressed (gcc, clang, msvc)
Specific Test Cases to Add¶
Priority 1 (Must Have Before Submission)¶
TEST_CASE("Nothrow guarantee for query_radius") {
grid.rebuild(particles);
REQUIRE_NOTHROW(grid.query_radius(10.0f, 0.0f, 0.0f, 0.0f));
REQUIRE_NOTHROW(grid.query_radius(-10.0f, 0.0f, 0.0f, 0.0f)); // Invalid
REQUIRE_NOTHROW(grid.query_radius(1e30f, 0.0f, 0.0f, 0.0f)); // Huge
}
TEST_CASE("2D Morton encoding at ±2^31 limit") {
cell_hash<2, int> hasher;
// At limit
cell_coord<2, int> at_limit{2147483647, 0}; // 2^31 - 1
auto hash1 = hasher(at_limit);
// Beyond limit (should work but may collide)
cell_coord<2, int> beyond{2147483647, 1};
auto hash2 = hasher(beyond);
// Document expected behavior here
}
TEST_CASE("3D infinite topology at ±2^21 limit") {
grid_config<3> cfg{
.cell_size = {1.0f, 1.0f, 1.0f},
.world_size = {10000000.0f, 10000000.0f, 10000000.0f},
.topology_type = topology::infinite
};
sparse_spatial_hash<Particle, 3> grid(cfg);
// Particles at cell coordinates ~±2^21
std::vector<Particle> particles = {
{2097151.0f, 0.0f, 0.0f, 0}, // Just under 2^21
{2097152.0f, 0.0f, 0.0f, 1} // Exactly 2^21
};
grid.rebuild(particles);
REQUIRE(grid.entity_count() == 2);
// Should work but document that beyond this, hash collisions increase
}
TEST_CASE("Constructor overflow protection: exact 1M cell limit") {
// Configure for exactly 1M cells (100^3)
grid_config<3> cfg{
.cell_size = {1.0f, 1.0f, 1.0f},
.world_size = {100.0f, 100.0f, 100.0f},
.topology_type = topology::bounded
};
sparse_spatial_hash<Particle, 3> grid(cfg);
// Should not overflow at exactly the cap
REQUIRE(grid.empty());
}
TEST_CASE("Constructor overflow protection: beyond 1M cells") {
// Configure for >1M cells (1000^3 = 1B cells)
grid_config<3> cfg{
.cell_size = {1.0f, 1.0f, 1.0f},
.world_size = {1000.0f, 1000.0f, 1000.0f},
.topology_type = topology::bounded
};
// Should cap reserve at 1M despite 1B total cells
sparse_spatial_hash<Particle, 3> grid(cfg);
// Verify it doesn't try to allocate 1B cells worth of memory
REQUIRE(grid.empty()); // Constructor succeeds
}
TEST_CASE("cell_entities returns consistent type for empty/occupied") {
grid.rebuild(particles);
cell_coord<3, int> empty_cell{99, 99, 99};
cell_coord<3, int> occupied_cell{5, 5, 5};
auto view1 = grid.cell_entities(empty_cell);
auto view2 = grid.cell_entities(occupied_cell);
// Both should be same type (ranges::view)
using Type1 = decltype(view1);
using Type2 = decltype(view2);
static_assert(std::same_as<Type1, Type2>);
}
TEST_CASE("Entity crosses boundary during incremental update") {
grid_config<2> cfg{
.cell_size = {10.0f, 10.0f},
.world_size = {100.0f, 100.0f},
.topology_type = topology::bounded
};
sparse_spatial_hash<Particle, 2> grid(cfg);
std::vector<Particle> particles = {
{45.0f, 45.0f, 0.0f, 0} // Near max boundary
};
grid.rebuild(particles);
auto initial_cell_count = grid.cell_count();
// Move beyond boundary - should clamp
particles[0].x = 105.0f;
particles[0].y = 105.0f;
grid.update(particles);
// Should still have 1 cell (clamped to edge)
REQUIRE(grid.cell_count() == 1);
REQUIRE(grid.entity_count() == 1);
// Verify entity is queryable at clamped position
auto results = grid.query_radius(10.0f, 49.9f, 49.9f);
REQUIRE_FALSE(results.empty());
}
TEST_CASE("Toroidal wrap during incremental update") {
grid_config<2> cfg{
.cell_size = {10.0f, 10.0f},
.world_size = {100.0f, 100.0f},
.topology_type = topology::toroidal
};
sparse_spatial_hash<Particle, 2> grid(cfg);
std::vector<Particle> particles = {
{45.0f, 45.0f, 0.0f, 0}, // Near edge
{-45.0f, -45.0f, 0.0f, 1} // Opposite side
};
grid.rebuild(particles);
REQUIRE(grid.cell_count() == 2);
// Move first particle across boundary - should wrap
particles[0].x = 55.0f; // Wraps to -45 region
particles[0].y = 55.0f;
grid.update(particles);
// Due to wrapping, might now be in same cell as particle 1
// Or nearby cell - verify wrapping occurred
REQUIRE(grid.entity_count() == 2);
// Verify wraparound query works
auto results = grid.query_radius(20.0f, 49.0f, 49.0f);
REQUIRE(results.size() >= 1);
}
Priority 2 (Highly Recommended)¶
TEST_CASE("for_each_pair with callback that throws") {
grid.rebuild(particles);
bool threw = false;
int pairs_processed_before_throw = 0;
try {
grid.for_each_pair(particles, 20.0f,
[&](std::size_t i, std::size_t j) {
pairs_processed_before_throw++;
if (pairs_processed_before_throw == 5) {
throw std::runtime_error("Test exception");
}
});
} catch (const std::runtime_error&) {
threw = true;
}
REQUIRE(threw);
REQUIRE(pairs_processed_before_throw == 5);
// Document: basic exception guarantee - some pairs processed,
// grid remains in valid state
REQUIRE(grid.cell_count() > 0); // Grid not corrupted
}
TEST_CASE("Update with entity count change triggers rebuild") {
std::vector<Particle> particles = {
{5.0f, 5.0f, 5.0f, 0},
{15.0f, 15.0f, 15.0f, 1}
};
grid.rebuild(particles);
REQUIRE(grid.entity_count() == 2);
// Add a particle
particles.push_back({25.0f, 25.0f, 25.0f, 2});
grid.update(particles); // Should trigger rebuild internally
REQUIRE(grid.entity_count() == 3);
REQUIRE(grid.cell_count() == 3);
}
TEST_CASE("Configuration with zero cell size is undefined") {
// Document: zero cell size is undefined behavior
// Constructor should ideally assert or throw
// For now, document that users must provide positive cell sizes
}
TEST_CASE("Empty range passed to rebuild") {
std::vector<Particle> empty;
grid.rebuild(empty);
REQUIRE(grid.empty());
REQUIRE(grid.cell_count() == 0);
REQUIRE(grid.entity_count() == 0);
// All operations should work on empty grid
auto results = grid.query_radius(100.0f, 0.0f, 0.0f, 0.0f);
REQUIRE(results.empty());
int pair_count = 0;
grid.for_each_pair(empty, 20.0f,
[&](std::size_t, std::size_t) { pair_count++; });
REQUIRE(pair_count == 0);
}
Testing Philosophy Observations¶
What the Tests Do Well¶
- Test the Contract: Most tests verify what the grid does, not how
-
Example: Tests verify incremental update produces same results as rebuild (behavior), not that it uses swap-and-pop (implementation)
-
Clear Test Names: Test names describe expected behavior
"Incremental update produces identical results to rebuild"✅-
Not:
"Test update function"❌ -
Realistic Scenarios: Large-scale tests (10K entities) verify real-world usage
Areas for Improvement¶
-
More Exact Assertions: Replace conservative
>=with exact expectations where possible -
Document Test Intent: When conservatism is necessary, explain why in comments
-
Regression Tests for Fixes: Each bug fix should have a dedicated test that would have caught the bug
Conclusion¶
Your test suite is solid but needs critical gaps filled before Boost submission:
Must Fix (Blocking): 1. Exception safety verification 2. Morton encoding limit testing at actual documented values 3. Overflow protection verification (not just "doesn't crash") 4. Recent fix verification (especially coordinate limits)
Should Fix (Highly Recommended): 5. Topology boundary transition tests 6. Iterator invalidation documentation and tests 7. Thread safety documentation 8. More exact assertions
Nice to Have: 9. Additional for_each_pair scenarios 10. Configuration edge cases 11. Better failure messages
Estimated Work: - Priority 1 fixes: 4-6 hours (20-25 new test cases) - Priority 2 fixes: 2-3 hours (10-15 new test cases) - Total: ~40-50 test cases to add
Final Grade After Fixes: A (Boost-ready)
Next Steps¶
- Create test_exception_safety.cpp with nothrow verification
- Create test_limits.cpp with Morton limit tests at actual boundaries
- Add regression tests for the 4 recent fixes
- Review all conservative assertions and make exact where possible
- Run with sanitizers (AddressSanitizer, UndefinedBehaviorSanitizer)
- Generate coverage report to find untested code paths
Would you like me to implement any of these specific test cases?