constrained-tests

name	constrained-tests
description	Slow-CI simulation — run unit tests on saturated CPU to reproduce CI-style flakiness locally. Suggest when new/reworked suite lean heavy on awaits (deferFulfillment, waitForConfirmation, TestClock, timeouts) or test fail only on CI. Not for every change.

Constrained test runs

CI runners shared + slow. Background tasks starve, awaits stretch, scheduler races flake there, pass locally. --constrained saturate CPU with hog tasks — same conditions, local.

When

• PR add/rework suite heavy on timing-sensitive async: deferFulfillment, waitForConfirmation, TestClock, transitionValues, timeouts.
• Test fail on CI, pass locally.
• Not routine changes, not sync suites — slow, no gain.

How

Full unit test workflow (what CI run):

swift run tools ci unit-tests --constrained

One suite, iterate on new tests (prefer while developing):

swift run tools ci run-tests --scheme UnitTests --test-name MyNewTests --constrained

Hog count automatic (2× cores). Suite survive ~10 constrained iterations → good shape.

Failures mean

Failure under constraint = real bug in test (sometimes code under test): assertion race async work, transient state observation missed, timeout too tight. Fix synchronisation, no blind timeout bump. Helpers in UnitTests/Sources/TestUtilities/ (deferFulfillment, deferFailure, waitForConfirmation). Wait on durable state, not transient.