fix(diskann): seed test RNGs to fix flaky test_diskann_basic#397
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`test_diskann_basic` and the other random-data tests in `crates/ruvector-diskann/src/index.rs` used `rand::thread_rng()`, so each CI run drew different vectors. The test asserts that the nearest neighbour of `vec-42` is `vec-42` itself; with unfavourable random draws the ANN graph traversal happened to settle on a near-duplicate (seen on main as `left: "vec-364"` vs `right: "vec-42"`) and the assertion failed. Fix: replace `thread_rng()` with `StdRng::seed_from_u64(0xD15CA77)` in `random_vectors()`, `test_recall_at_10`, and `test_scale_5k`. Output is fully deterministic across runs and platforms; verified locally with three repeats of `test_diskann_basic` and the full lib-test suite (17/17 passing in 49.6s). No production-code changes; tests-only.
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Problem
Workspace-CI on main started failing
Tests (vector-index)after theACORN/RaBitQ-WASM merges (#391, #394) — not due to the new code, but
because
ruvector-diskann::index::tests::test_diskann_basicis flaky.The test draws 500 random 32-dim vectors, queries with
vec-42, andasserts the nearest neighbour is
vec-42itself. Withrand::thread_rng()(unseeded), CI run 24976593452 drew anunlucky distribution where the Vamana graph traversal returned
vec-364instead and the assertion failed.Fix
Replace
thread_rng()withStdRng::seed_from_u64(0xD15CA77)in thethree test-only RNG sites in
crates/ruvector-diskann/src/index.rs:random_vectors()— used bytest_diskann_basic,test_diskann_with_pq,test_diskann_save_loadtest_recall_at_10test_scale_5kNow fully deterministic across runs and platforms.
Verification
cargo test -p ruvector-diskann --lib→ 17/17 pass (49.6s)cargo test -p ruvector-diskann --lib test_diskann_basic×3 → allpass with identical timings (≈0.1s each)
No production-code changes; this is tests-only.