Glossary

Worker — a Python process (gw0, gw1, ...) running your project's interpreter with the vendored pytest core; executes tests and streams reports to the orchestrator.

Orchestrator — the rstest binary: spawns workers, dispatches tests, merges results, renders output.

Master / controller — pytest-xdist's term for its central coordinating process. rstest has no such process — the Rust orchestrator plays that role — so "master-side" xdist hooks are emulated per worker. See xdist hook emulation.

Vendored core — the unmodified copy of pytest shipped inside rstest_worker._vendor; provides all test semantics. Never conflicts with an installed pytest.

Item dispatch — distributing individual tests (not files) to workers by index into the verified collection.

Long-pole — a test whose duration exceeds the ideal per-worker share; it caps the wall time of any parallel run. Dispatched first, individually.

Chunk — a contiguous run of collection order dispatched as one unit, preserving module-fixture locality.

nextitem invariant — a worker never runs its final pending test until it knows the successor (teardown scoping requires it); queues must always end explicitly.

Designate — the worker chosen to host the serial phase and to ship the full collection id list.

Serial phase — @pytest.mark.serial tests running exclusively on the designate after all other workers finish.

Flaky — a test that failed and then passed within the --reruns budget; reported green but counted and listed.

Byte-exact mode — -n 0 and -n 1 are identical: one in-process pytest session, no worker, no [gwN] attribution, byte-exact pytest behavior — the compatibility anchor. There is no worker identity below -n 2 (unlike pytest-xdist, whose -n 1 spawns a gw0 worker — see xdist migration). The flags that need pytest's own terminal (--co, -s, --capture, --pdb, --trace) switch to this mode automatically. See Compatibility for the guarantee and Architecture for how it falls back. One opt-in exception: passing --reruns runs -n 0/-n 1 as a degenerate one-worker pool so retries fire, trading byte-exactness for the reruns you asked for.

Selection — the set of tests chosen to run; under --changed, derived from the import graph.