Features

Everything pytest does (via a vendored pytest core), plus:

New here? Start with three

rstest (parallel by default), rstest --doctor (why the suite is slow), and rstest --watch (instant reruns on save). Evaluating a switch from pytest? rstest --try gives a 30-second verdict. The full surface:

Feature	Flag / API	Notes
Parallel by default	-n auto (default)	suite-aware worker count; -n 0 = byte-exact pytest session
Migration check	--try, --migrate-check	--try runs pytest vs rstest -n auto and prints the "should I switch?" verdict; --migrate-check classifies parallel-only failures
Test-granular scheduling	--dist load (default)	duration cache runs slowest tests first; module locality preserved
Affinity modes	--dist loadfile/loadscope/loadgroup	file, fixture-scope, or xdist_group affinity (xdist-compatible)
Broadcast mode	--dist each	every worker runs the full suite (xdist --dist=each) for multi-environment validation; outcomes keyed [gwN]
Serial escape hatch	@pytest.mark.serial	exclusive, after the parallel phase
Crash recovery	automatic	crashed test reported failed; worker respawns; run completes
Flaky handling	--reruns N, @pytest.mark.flaky, --only-rerun	failed-then-passed = flaky (green run, counted, listed); crash-aware. --reruns needs -n ≥ 2 — ignored under -n 0/1
Suite diagnostics	--doctor, --doctor-json	wait-bound tests, parallel floor, fixture hotspots, slowest files
Live status footer	automatic on a terminal	per-worker current test + elapsed, progress + ETA
Output styles	--output dots/verbose/bar/github/json (+ gitlab/buildkite/teamcity/azure/tap — see CLI)	bar (the TTY default) = pytest-sugar-style per-test lines, inline failures, progress bar — works under the parallel pool. github emits CI annotations; json is a live NDJSON event stream
Watch mode	--watch	targeted reruns on save via the import graph
Smart selection	--changed[=REV]	run only tests affected by changed files
Coverage	--cov, --cov-report, --cov-fail-under	pytest-cov, combined across workers
Global fail-fast	-x, --maxfail=N	coordinated across all workers
Failure reruns cache	--lf, --ff	merged across workers
Hang watchdog	--worker-timeout SECS	kills + replaces a worker stuck on one test
Project config	[tool.rstest] in pyproject	committed defaults for -n, --dist, --reruns, timeout
Worker attribution	automatic	[gwN] on -v lines and failure headers
JUnit XML	--junitxml	rendered from merged results; flaky tests flagged via property
Machine-readable results	--report-json	per-test outcome snapshot

Everything else — fixtures, parametrize, marks, conftest, plugins, ini config, the pytest flag surface — behaves as pytest because it is pytest underneath. See Compatibility.