Testing

The funnel test suite covers three dimensions: correctness, stress, and the hylomorphism property. All tests run for both queue strategies (PerWorker and Shared) via policy-generic test helpers.

Correctness

Verify that funnel produces the same result as the sequential Fused executor across all named policy presets:

• Default, SharedDefault, WideLight, LowOverhead, PerWorkerArrival
• Tree sizes: 60 nodes (bf=4), 200 nodes (bf=6, bf=20)
• Zero workers (all work done by the caller thread)
• Adjacency-list trees (callback-based treeish_visit)
• Wide-tree stress (500 iterations, pool reused)

Stress

High iteration counts to catch timing-sensitive races:

• 1500 runs per policy on a reused pool
• Pool lifecycle: 5000 create/destroy cycles
• Mixed policy: 50k iterations switching between PerWorker and Shared on the same pool (mimics criterion benchmark pattern)
• 20k noop iterations each: Shared + OnFinalize and Shared + OnArrival at criterion warmup intensity
• Interleaved policies: 12.5k iterations alternating four policies on one pool

These tests exercise the dispatch → in_job latch protocol under the exact conditions that previously triggered SIGSEGV (high-iteration noop folds with rapid pool reuse).

Interleaving proof

The hylomorphism property: fold interleaves with traversal across subtrees. While one subtree is being visited (walk down), another subtree’s results are being accumulated (cascade up).

The test uses a lock-free TraceLog (2048-entry bounded log, atomic sequence counter) to record visit and accumulate operations with thread IDs and subtree tags. After 20 attempts on an 85-node tree, the test asserts that cross-subtree interleaving occurred — proving that the fold is not merely parallel but genuinely fused.