Isolate expect.assertions state per test.concurrent by arronKler · Pull Request #16340 · jestjs/jest

arronKler · 2026-08-14T10:37:40Z

Summary

expect.assertions(n) and expect.hasAssertions() store their counters on a single global matcher state object. When two test.concurrent cases run at the same time, they increment and check the same assertionCalls field, so a pair of tests that each declare expect.assertions(1) fails with "Expected one assertion to be called but received two assertion calls."

jest-circus already exposes the active test id through currentConcurrentTestName (backed by AsyncLocalStorage). expect.getState() / setState() now keep assertion-related fields on a per-test view keyed by that name, so each concurrent test has its own budget.

Fixes #14263

Test plan

Unit tests in packages/expect interleave two synthetic concurrent names and assert that each test only sees its own assertion count / hasAssertions result.
Unit tests in jest-circus drive eventHandler test_done for two overlapping concurrent names.
e2e fixtures under e2e/circus-concurrent cover passing concurrent + sequential expect.assertions / expect.hasAssertions, and a sibling that exceeds its budget without failing the other test.
FORCE_COLOR=1 yarn jest packages/expect/src/__tests__/assertionCounts.test.ts packages/jest-circus/src/legacy-code-todo-rewrite/__tests__/concurrentAssertions.test.ts e2e/__tests__/circusConcurrent.test.ts

expect.assertions and expect.hasAssertions stored their counters on a single global matcher state object. Concurrent tests therefore shared assertion counts and failed with "expected one assertion but received two". Keep those fields on a per-test view keyed by the circus AsyncLocalStorage test name so each test.concurrent has its own budget. Fixes jestjs#14263

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linux-foundation-easycla · 2026-08-14T10:37:46Z

❌ - login: @arronKler / name: Arron Zou. The commit (54fd8bf, c4f3ca0, ee43aa0) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

CI Static Checks failed: assigning through IsolatedStateKey was typed as never.

pkg-pr-new · 2026-08-14T10:55:02Z

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commit: 54fd8bf

arronKler · 2026-08-14T12:28:40Z

recheck

soltonigiri

Thanks for working on this. I used b654d7e as the main baseline and 54fd8bf as the PR head. The original reproduction with distinct titles fails on the baseline and passes on the PR head. The PR’s focused command passes all 23 tests. I also ran build:js, build:ts, typecheck:tests, ESLint, Prettier, the changelog check, and git diff --check successfully.

I found one correctness gap that I think needs to be addressed before merge: the isolated matcher state is keyed by the full test-name string, so concurrent tests with the same full title still share assertion state. The reproduction and details are inline.

soltonigiri · 2026-08-16T01:22:58Z

+
+const getIsolatedStateView = (testName: string): MatcherState => {
+  const store = getMatchersObject();
+  const existing = store.isolatedMatcherStates.get(testName);


I think this needs a collision-free execution identity rather than the full test-name string.

testName ultimately comes from testNameStorage.run(getTestID(child), ...), and getTestID() is the joined title path. Jest’s runtime does not reject duplicate titles, so two concurrent test entries with the same full title use the same isolatedMatcherStates entry.

On 54fd8bf, I reproduced this with two test.concurrent('duplicate name', ...) cases. A barrier ensures that each case calls expect.assertions(1) and makes exactly one assertion before either case completes. One case then fails with:

Expected one assertion to be called but received two assertion calls.

Changing only one title makes the fixture pass.

Could we carry a separate collision-free identity alongside the display name through the async context and use that as the isolation key? A duplicate-title E2E regression test would cover this case.

good catch! 😀 I agree

SimenB

The duplicate-title collision @soltonigiri found is a symptom of the shape, not a bug to patch. I'd rather we removed the key than made it collision-free.

jest-circus has AsyncLocalStorage (run.ts:35). If the store held the per-test state object instead of a name string, expect would just read it:

const getState = () => getCurrentTestState?.() ?? getMatchersObject().state;

That drops the isolatedMatcherStates map, the keying question, the eviction question, and the Proxy in one go. Two things that matter here:

run.ts:146 wraps every test in the ALS, not just concurrent ones, so today's Proxy is on the assertion path for all tests. expect/src/index.ts:303 spreads getState() on every expect() call, which runs the ownKeys + getOwnPropertyDescriptor traps per key. I measured ~+4.4µs per assertion; expect(1).toBe(1) is ~11µs to begin with, so that's roughly +40% across the board.
Nothing ever deletes from the map, and resetAssertionsLocalState doesn't clear expectedAssertionsNumberError, so every test title that called expect.assertions leaves a retained Error with its stack until the file is done.

Neither survives if the state travels in the ALS store.

One field can come off the list either way: currentTestName doesn't need isolating, since jest-snapshot/src/index.ts:292 already prefers currentConcurrentTestName?.() over it. Isolating it only means reads from outside the ALS scope now see undefined.

SimenB · 2026-08-18T08:27:48Z

+  globalState: MatcherState,
+  isolated: IsolatedMatcherState,
+): MatcherState =>
+  new Proxy(globalState, {


this wraps every single test rather than just concurrent ones. is that needed? seems like a bit of overreach that will impact waaaaay more tests than the ones that needs this change

SimenB · 2026-08-18T08:28:26Z

+
+  const isolated = createIsolatedMatcherState();
+  const view = createIsolatedStateView(store.state, isolated);
+  store.isolatedMatcherStates.set(testName, {isolated, view});


this grows infinitely - maybe clear it somehow after tests are done running?

SimenB · 2026-08-18T08:32:11Z

Oh, and also please sign the CLA 🙂

github-actions Bot added the require-changelog If a PR does requires a changelog entry label Aug 14, 2026

arronKler added 2 commits August 14, 2026 18:39

docs: link changelog entry to the pull request

c4f3ca0

fix: type isolated matcher state assignment for tsc

54fd8bf

CI Static Checks failed: assigning through IsolatedStateKey was typed as never.

soltonigiri reviewed Aug 16, 2026

View reviewed changes

SimenB requested changes Aug 18, 2026

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Isolate expect.assertions state per test.concurrent - #16340

Isolate expect.assertions state per test.concurrent#16340
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