fix(lint/useExpect): reject asymmetric matchers and utilities as assertions by omar-y-abdi · Pull Request #9455 · biomejs/biome

omar-y-abdi · 2026-03-12T08:30:40Z

Summary

useExpect produced false negatives for Vitest constructs like expect.stringContaining(), expect.extend(), and expect.not.objectContaining(). These are asymmetric matchers and utilities, not assertions, but the rule counted them as valid assertions and did not flag the test.

The root cause was in is_expect_expression in playwright.rs. The JsStaticMemberExpression branch unconditionally recursed on the object expression, so any expect.anything() pattern was treated as a valid assertion chain.

Fix

When the object of a static member expression is a bare expect identifier (not a call like expect(value)), the member name is now checked against an allowlist of assertion-qualifying members: soft, poll, assertions, hasAssertions. All other members on bare expect (asymmetric matchers, extend, not prefix for negated matchers) are correctly rejected.

Chained assertions like expect(value).not.toBe(1) and expect.soft(page).toBeVisible() are unaffected because their object is a call expression, not a bare identifier.

Test plan

Added invalid/asymmetric-matchers.js with 3 cases: expect.stringContaining(), expect.extend(), expect.not.objectContaining() — all now correctly flagged
Added valid/assertion-counts.js with 5 cases: expect.assertions(), expect.hasAssertions(), expect.assertions(0), expect.soft(), expect.poll() — all correctly pass
All 6 use_expect spec tests pass
All 7 is_expect_call unit tests pass (no regression)
All 66 no_playwright_* spec tests pass (no regression)
All 2 no_conditional_expect spec tests pass (no regression)

Closes #9174

AI disclosure

This PR was written with assistance from Claude Code (code comprehension, tracing the bug through the AST traversal logic, and drafting the implementation). All code was reviewed and verified by the author.

…rtions is_expect_expression treated any expect.XYZ() pattern as a valid assertion because the JsStaticMemberExpression branch unconditionally recursed on the object. This caused false negatives for expect.stringContaining(), expect.extend(), expect.not.objectContaining(), and similar constructs that are not assertions. When the object is a bare expect identifier, check the member name against an allowlist of assertion-qualifying members (soft, poll, assertions, hasAssertions). Everything else on bare expect is now correctly rejected. Closes biomejs#9174

changeset-bot · 2026-03-12T08:30:45Z

🦋 Changeset detected

Latest commit: ee548ac

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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ematipico

Changeset is missing. The link to how to create was in the PR template, which was wiped out. I leave that to you

crates/biome_js_analyze/src/frameworks/playwright.rs

coderabbitai · 2026-03-12T08:37:08Z

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crates/biome_js_analyze/src/frameworks/playwright.rs

Walkthrough

Tightens detection in the useExpect lint rule: static expect member accesses are now counted as assertions only when the member name is exactly soft, poll, assertions, or hasAssertions. Other expect.XYZ usages (including asymmetric matchers like expect.stringContaining and helpers like expect.extend) are no longer treated as assertions. Adds tests covering invalid asymmetric-matcher usages and valid assertion-count APIs. No exported or public signatures changed.

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ematipico
dyc3

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: rejecting asymmetric matchers and utilities as valid assertions in the useExpect lint rule.
Description check	✅ Passed	The description thoroughly explains the problem, root cause, fix, and test coverage, clearly relating to the changeset.
Linked Issues check	✅ Passed	The PR addresses all primary coding objectives from issue `#9174`: rejects asymmetric matchers and utilities while preserving valid assertion syntaxes, with comprehensive test cases.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the useExpect rule as specified in issue `#9174`; no extraneous modifications detected.

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🧹 Nitpick comments (1)

crates/biome_js_analyze/tests/specs/nursery/useExpect/invalid/asymmetric-matchers.js (1)
3-17: Consider adding a few more asymmetric matchers for completeness (optional).

The fix rejects all non-allowlisted members generically, so exhaustive testing isn't essential. However, adding one or two more cases (e.g., expect.anything(), expect.arrayContaining()) would strengthen confidence and serve as documentation of the intended behaviour.
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In
`@crates/biome_js_analyze/tests/specs/nursery/useExpect/invalid/asymmetric-matchers.js`
around lines 3 - 17, Add one or two extra test cases that use other asymmetric
matchers to broaden coverage: e.g., create a test similar to "only asymmetric
matcher, not an assertion" that assigns expect.anything() to a variable and
another that assigns expect.arrayContaining([1,2]) (or expect.objectContaining
with nested asymmetric) to exercise arrayContaining; place them near the
existing tests (functions test/it using matcher variables) so names like "only
asymmetric matcher, not an assertion" / "negated asymmetric matcher is not an
assertion" are extended with new cases and the new matcher variables mirror the
existing pattern.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In
`@crates/biome_js_analyze/tests/specs/nursery/useExpect/invalid/asymmetric-matchers.js`:
- Around line 3-17: Add one or two extra test cases that use other asymmetric
matchers to broaden coverage: e.g., create a test similar to "only asymmetric
matcher, not an assertion" that assigns expect.anything() to a variable and
another that assigns expect.arrayContaining([1,2]) (or expect.objectContaining
with nested asymmetric) to exercise arrayContaining; place them near the
existing tests (functions test/it using matcher variables) so names like "only
asymmetric matcher, not an assertion" / "negated asymmetric matcher is not an
assertion" are extended with new cases and the new matcher variables mirror the
existing pattern.

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crates/biome_js_analyze/tests/specs/nursery/useExpect/invalid/asymmetric-matchers.js.snap is excluded by !**/*.snap and included by **
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crates/biome_js_analyze/src/frameworks/playwright.rs
crates/biome_js_analyze/tests/specs/nursery/useExpect/invalid/asymmetric-matchers.js
crates/biome_js_analyze/tests/specs/nursery/useExpect/valid/assertion-counts.js

…th docs link

omar-y-abdi · 2026-03-12T08:39:04Z

Addressed both review items:

Replaced the issue reference in the comment with a link to the Vitest asymmetric matchers docs
Added changeset file

omar-y-abdi

Happy to help out

codspeed-hq · 2026-03-12T13:49:45Z

Merging this PR will not alter performance

✅ 58 untouched benchmarks
⏩ 156 skipped benchmarks¹

_{Comparing omar-y-abdi:fix/use-expect-false-negatives (c221d57) with main (4305e9d)}

156 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

.changeset/fix-use-expect-false-negatives.md

Co-authored-by: Naoki Ikeguchi <me@s6n.jp>

omar-y-abdi · 2026-03-14T14:30:03Z

@ematipico Hey, this is ready to merge whenever you get a chance.

dyc3 · 2026-03-17T13:39:37Z

@omar-y-abdi there is still failing CI

github-actions bot added A-Linter Area: linter L-JavaScript Language: JavaScript and super languages labels Mar 12, 2026

ematipico requested changes Mar 12, 2026

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fix: address review feedback — add changeset and replace issue ref wi…

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…th docs link

omar-y-abdi requested a review from ematipico March 12, 2026 08:44

omar-y-abdi commented Mar 12, 2026

View reviewed changes

ematipico approved these changes Mar 12, 2026

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omar-y-abdi and others added 3 commits March 12, 2026 16:39

Update .changeset/fix-use-expect-false-negatives.md

a51461c

Co-authored-by: Naoki Ikeguchi <me@s6n.jp>

Merge branch 'main' into fix/use-expect-false-negatives

8bf71e2

Merge branch 'main' into fix/use-expect-false-negatives

c221d57

dyc3 and others added 2 commits March 20, 2026 15:10

chore: lints

e0b56c3

[autofix.ci] apply automated fixes

ee548ac

dyc3 merged commit 1710cf1 into biomejs:main Mar 20, 2026
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fix(lint/useExpect): reject asymmetric matchers and utilities as assertions#9455

fix(lint/useExpect): reject asymmetric matchers and utilities as assertions#9455
dyc3 merged 7 commits intobiomejs:mainfrom
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Summary

Fix

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