Ruby "rspec --bisect" Fails or Stalls in CI

rspec --bisect tries to minimize the set of examples that reproduce an order-dependent failure, but it only works when the failure is deterministic for a given order. Flaky, parallel, or externally-stateful tests make bisect fail or loop.

What this error means

rspec --bisect cannot narrow the failure - it reports it could not reproduce, runs indefinitely, or yields an unhelpful minimal set. The underlying test passes and fails inconsistently for the same order.

rspec output

Bisect started using options: "--seed 12345"
Running suite to find failures... 1 failure found
Starting bisect with 1 failing example and 240 non-failing examples.
Bisect aborted! The bisect process failed to reproduce the failure.

Common causes

Failure is not deterministic for an order

Bisect assumes a given example order reproduces the failure every time. If the failure depends on wall-clock time, randomness, or external state, it does not reproduce reliably and bisect aborts.

Parallelism or shared state interferes

Running bisect against a suite that uses parallel workers or shared global state breaks the one-order-one-result assumption bisect relies on.

How to fix it

Make the failure reproducible first

Pin the seed and run serially so the order-dependent failure is deterministic before bisecting.

Terminal

bundle exec rspec --seed 12345 --order defined   # confirm it fails
bundle exec rspec --bisect --seed 12345

Remove non-determinism, then bisect

Run bisect serially (not under parallel_tests).
Eliminate reliance on real time/randomness in the suspect specs (freeze time, seed RNG).
Ensure global state is reset between examples so order is the only variable.

How to prevent it

Keep tests independent and free of shared global state.
Run --bisect serially with a fixed seed.
Stub time/randomness so order is the only source of failure.