Inspired by Django's internal bisect tool, easily bisect your test suite and find test-on-test failures.
More importantly: Test FOO fails when run when test X, bisect will tell you what X is.
And get some sometimes-useful output:
Bisecting against tests.integration.disqus.forums.api.endpoints.tests:ForumEndpointTest.test_list_users ├── Pass 1: Running 1410 test(s) in 2 chunks... │ ├── Chunk 1a: Running 780 tests │ │ └── Tests completed in 371.578s (failure found) │ ├── Chunk 1b: Running 631 tests │ │ └── Tests completed in 224.881s (failure found) │ └── Multiple sources of failure found (2 chunks)
(In our above case, our test suite is actually broken, so it's failing to find a way to bisect)