🐛(vitest) Fix runtime exception with `test.each` by dubzzz · Pull Request #6804 · dubzzz/fast-check

dubzzz · 2026-03-31T22:18:54Z

When building the enriched test function, the each method was extracted from testFnExtended (created by createTaskCollector) without proper this binding. This caused a 'Cannot read properties of undefined (reading withContext)' error when calling test.each().

Fix: use the original vitest testFn's each method with proper binding, since each is a standard vitest feature that doesn't need fast-check wrapping.

Fixes #6798

Description

Fixes #issue-number

Checklist

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…nction When building the enriched test function, the each method was extracted from testFnExtended (created by createTaskCollector) without proper this binding. This caused a 'Cannot read properties of undefined (reading withContext)' error when calling test.each(). Fix: use the original vitest testFn's each method with proper binding, since each is a standard vitest feature that doesn't need fast-check wrapping. Fixes #6798 Co-authored-by: Nicolas DUBIEN <[email protected]>

changeset-bot · 2026-03-31T22:18:58Z

🦋 Changeset detected

Latest commit: e2e0f70

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

This PR includes changesets to release 1 package

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pkg-pr-new · 2026-03-31T22:23:09Z

@fast-check/examples

@fast-check/ava

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fast-check

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@fast-check/jest

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@fast-check/packaged

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@fast-check/poisoning

npm i https://pkg.pr.new/@fast-check/poisoning@6804

@fast-check/vitest

npm i https://pkg.pr.new/@fast-check/vitest@6804

@fast-check/worker

npm i https://pkg.pr.new/@fast-check/worker@6804

commit: e2e0f70

Apply the same .bind(testFn) fix to the non-each branch of the loop, ensuring methods like skip, only, concurrent etc. also retain proper this context when accessed through the enriched test function. Co-authored-by: Nicolas DUBIEN <[email protected]>

dubzzz · 2026-03-31T22:25:32Z

-          ? buildTest((testFn as any)[key], testFnExtended[key] as any, fc, new Set([...ancestors, key]))
-          : testFnExtended[key];
+          ? buildTest(((testFn as any)[key] as (...args: unknown[]) => unknown).bind(testFn), testFnExtended[key] as any, fc, new Set([...ancestors, key]))
+          : ((testFn as any)[key] as (...args: unknown[]) => unknown).bind(testFn);


@claude bind extended fn too?

Claude finished @dubzzz's task in 40s —— View job

Read the code around line 149 to understand what needs binding

Implement the fix

Push the change

Added .bind(testFnExtended) to the testFnExtended[key] argument in the recursive buildTest call on line 148, so the extended fn also retains proper this context.

Change: b809fde

Co-authored-by: Nicolas DUBIEN <[email protected]>

Applied by GitHub Action workflow: PR Format Run ID: 23822582479 Target PR: 6804

claude · 2026-04-01T19:49:43Z

Claude finished @dubzzz's task in 11m 2s —— View job

Diagnose why 14 tests broke after binding changes
Fix the issue in TestBuilder.ts
Push the fix

Root cause

The previous commits had two issues:

.bind() strips own properties: testFnExtended[key].bind(testFnExtended) creates a new bound function that loses all own properties (like skip, only, concurrent, etc.). So when buildTest recurses into it, Object.getOwnPropertyNames() finds nothing, the recursion stops early, and .prop is never added to sub-levels → test.concurrent.prop is not a function.
testFn[key] can be undefined: testFn (the original vitest function) may not have all keys that testFnExtended (from createTaskCollector) has. Accessing undefined[key] then throws.

Fix

Don't bind testFnExtended[key] — it's only used for property enumeration and is already wrapped in a closure (line 158), so binding is unnecessary
Guard testFn[key] access with a null check for safety

Change: cb7a99d

|

Don't bind testFnExtended[key] as .bind() creates a new function without own properties, breaking property enumeration in recursive calls. Guard testFn[key] access against testFn being undefined/null. Co-authored-by: Nicolas DUBIEN <[email protected]>

Co-authored-by: Nicolas DUBIEN <[email protected]>

Bind testFnExtended[key] to preserve proper this context, using Object.defineProperties to copy own property descriptors back onto the bound function so that Object.getOwnPropertyNames still finds sub-properties for recursion. Re-add null check on testFn since it can be undefined at deeper recursion levels. Co-authored-by: Nicolas DUBIEN <[email protected]> Co-authored-by: Claude Opus 4.6 <[email protected]>

Drop Object.defineProperties wrapper and use simple .bind() matching the pattern used for testFn binding. Co-authored-by: Nicolas DUBIEN <[email protected]>

Applied by GitHub Action workflow: PR Format Run ID: 23925298609 Target PR: 6804

rushelex · 2026-04-23T13:37:22Z

@dubzzz Check out PR #6910 with a fix for this PR

…er (#6910) Fixes PR #6804. The `each` method (e.g. `it.each` / `test.each`) in Vitest requires a valid `this` context, as it uses `this` internally to access class methods. When assigning via `testFn[key]`, the context was lost, leading to errors when calling `it.each(...)`. Fix: explicitly bind the method to `testFn` via `.bind(testFn)`, ensuring the correct context is used when calling.

codecov · 2026-04-23T14:37:11Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.75%. Comparing base (cabaab6) to head (e2e0f70).
⚠️ Report is 52 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6804      +/-   ##
==========================================
- Coverage   94.82%   94.75%   -0.08%     
==========================================
  Files         209      211       +2     
  Lines        5665     5778     +113     
  Branches     1489     1526      +37     
==========================================
+ Hits         5372     5475     +103     
- Misses        285      295      +10     
  Partials        8        8

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dubzzz changed the title ~~🐛(vitest) Fix test.each TypeError by binding each to original test function~~ 🐛(vitest) Fix runtime exception with test.each Mar 31, 2026

dubzzz commented Mar 31, 2026

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Comment thread packages/vitest/src/internals/TestBuilder.ts

dubzzz commented Mar 31, 2026

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github-actions Bot and others added 2 commits March 31, 2026 22:26

🐛(vitest) Bind testFnExtended methods in recursive buildTest calls

b809fde

Co-authored-by: Nicolas DUBIEN <[email protected]>

💄 Format code with prettier

7d88e02

Applied by GitHub Action workflow: PR Format Run ID: 23822582479 Target PR: 6804

dubzzz enabled auto-merge (squash) March 31, 2026 22:42

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dubzzz commented Apr 1, 2026

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Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

github-actions Bot and others added 2 commits April 1, 2026 20:04

♻️(vitest) Drop unnecessary null check on testFn

2e48eeb

Co-authored-by: Nicolas DUBIEN <[email protected]>

dubzzz commented Apr 1, 2026

View reviewed changes

Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

♻️(vitest) Simplify testFnExtended binding in recursive buildTest

26e6676

Drop Object.defineProperties wrapper and use simple .bind() matching the pattern used for testFn binding. Co-authored-by: Nicolas DUBIEN <[email protected]>

dubzzz commented Apr 1, 2026

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Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

Update packages/vitest/src/internals/TestBuilder.ts

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dubzzz commented Apr 1, 2026

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Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

Update packages/vitest/src/internals/TestBuilder.ts

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dubzzz commented Apr 2, 2026

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Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

Comment thread packages/vitest/src/internals/TestBuilder.ts Outdated

dubzzz and others added 3 commits April 3, 2026 00:38

Update packages/vitest/src/internals/TestBuilder.ts

adad209

Update packages/vitest/src/internals/TestBuilder.ts

f642f55

💄 Format code with prettier

3082d3a

Applied by GitHub Action workflow: PR Format Run ID: 23925298609 Target PR: 6804

dubzzz added the force-build-status-execution label Apr 2, 2026

dubzzz added force-build-status-execution and removed force-build-status-execution labels Apr 2, 2026

Merge branch 'main' into claude/issue-6798-20260331-2201

44c1ba9

rushelex mentioned this pull request Apr 23, 2026

🐛(vitest) Bind each method to preserve this context in test builder #6910

Merged

fix typings

e2e0f70

dubzzz disabled auto-merge April 28, 2026 20:53

dubzzz enabled auto-merge (squash) April 28, 2026 20:53

dubzzz merged commit f95a6bd into main Apr 28, 2026
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dubzzz deleted the claude/issue-6798-20260331-2201 branch April 28, 2026 20:59

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🐛(vitest) Fix runtime exception with `test.each`#6804

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