Add flake_cluster: cluster tests that flake together (co-failure Jaccard)#412
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…ard) Flaky tests are rarely independent - a wobbly fixture or noisy dependency makes a group fail in the same runs (~75% of flaky tests cluster). Ranking tests one-by-one by flip rate misses that shared root cause. Measure how often each pair fails in the same runs (Jaccard over their failing-run sets) and group tests above a threshold into connected clusters with a cohesion score. Pure stdlib over a list of failed-test sets.
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| Metric | Results |
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| Complexity | 43 |
| Duplication | 0 |
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Why
Flaky tests are rarely independent: a wobbly shared fixture, a slow dependency or a noisy environment makes a group of tests fail in the same runs (research finds ~75% of flaky tests fall into co-failure clusters). Ranking tests one-by-one by flip rate misses that shared root cause.
flake_clustermeasures how often each pair of tests fails in the same runs — Jaccard similarity over the set of runs each failed in — and groups tests above a threshold, so you chase one root cause instead of N symptoms.cofailure_pairs— test pairs that fail together above a Jaccard thresholdfailure_clusters— connected clusters of co-failing tests with a cohesion score (mean pairwise Jaccard)Third item of the test-robustness lane. Input is a list of runs, each the test names that failed in it.
Design
text_similarity.jaccardis n-gram string similarity (different), so set-Jaccard stays internal. Every function under CC 10 (radon-clean).__all__→AC_failure_clusters/AC_cofailure_pairs→ read-onlyac_*MCP tools → Script Builder (Testing). Qt-free verified;pytest.approxfor cohesion (no float==).Tests
test/unit_test/headless/test_flake_cluster_batch.py— clusters group co-failing tests (cohesion 1.0), singleton excluded bymin_size,min_size=1keeps singletons, high threshold keeps only perfect co-failure,cofailure_pairsscores + sort + count, empty / no-co-failure cases, the executor paths + 5-layer wiring. 9 passed.