test: implement parity fuzzing

[mfkrause]

Summary by CodeRabbit

• Chores

  • Added property-based testing framework dependency.

• Tests

  • Enhanced testing infrastructure with comprehensive platform compatibility verification capabilities, including automated property-based fuzzing, improved test utilities, and expanded mock implementations for cross-platform validation.

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Walkthrough

Adds a property-based fuzz test suite to the React Native Boost parity test harness using fast-check. Introduces shared normalize/flattenStyle utilities, a writeAndImportFresh module loader, a PlatformOS type, vocabulary/generator modules for JSX spec construction, a diff.ts for order-insensitive prop comparison, and a fuzz.test.ts with three test modes.

Changes

Parity Fuzz Testing

Layer / File(s)	Summary
Shared parity infrastructure src/plugin/__tests__/parity/normalize.ts, src/plugin/__tests__/parity/generated.ts, src/plugin/__tests__/parity/mocks/Platform.ts, src/plugin/__tests__/parity/mocks/react-native.ts, src/plugin/__tests__/parity/parity.test.ts	Introduces flattenStyle/normalize for prop comparison, writeAndImportFresh for cache-busted dynamic module reloading, and the PlatformOS type alias in the Platform mock. The react-native mock's StyleSheet.flatten is changed from an identity stub to delegate to flattenStyle. Existing parity.test.ts imports normalize from the new shared module and removes its local implementations.
Harness refactoring with preamble support src/plugin/__tests__/parity/boost.ts, src/plugin/__tests__/parity/wrapper.ts	boost.ts and wrapper.ts replace counter-based file-write-and-import with writeAndImportFresh, update os parameter typing to PlatformOS, and add an optional preamble parameter to captureBoost, captureWrapper, and captureWrapperHosts.
Fuzz vocabulary and JSX spec generator src/plugin/__tests__/parity/fuzz/vocabulary.ts, src/plugin/__tests__/parity/fuzz/generator.ts	vocabulary.ts exports PropSpec interface and three fast-check arbitrary arrays (TEXT_VOCAB, TEXT_BLACKLIST_SAMPLE, VIEW_VOCAB) covering accessibility props, style generators, and ARIA translations. generator.ts exports ElementSpec types, elementSpecArb/platformArb, and a render(spec) function that converts specs into { preamble, jsxBody } by hoisting dynamic attrs and children into const declarations.
Diff utilities and fuzz test suite src/plugin/__tests__/parity/fuzz/diff.ts, src/plugin/__tests__/parity/fuzz/fuzz.test.ts	diff.ts adds canonical (recursive key-sorted normalizer) and divergingKeys for order-insensitive prop comparison. fuzz.test.ts implements runCase to classify boost vs wrapper output as skipped/match/divergence, three test modes: property-based (fc.asyncProperty with optimization-rate assertion), exhaustive 3×3×3 Text accessibility matrix, and discovery mode (gated by FUZZ_DISCOVER=1) that catalogs divergence classes by frequency.
devDependency and Vitest config package.json, src/plugin/__tests__/parity/vitest.config.parity.mts	Adds fast-check ^4.8.0 to devDependencies and extends the Vitest parity config include list to add ./fuzz/fuzz.test.ts.

Sequence Diagram(s)

sequenceDiagram
  participant fc as fast-check
  participant gen as generator.ts
  participant boost as captureBoost
  participant wrapper as captureWrapper
  participant diff as diff.ts
  participant test as fuzz.test.ts

  fc->>gen: sample elementSpecArb × platformArb
  gen-->>test: { preamble, jsxBody, os }
  test->>boost: captureBoost(os, jsxBody, preamble)
  boost-->>test: BoostBailed | BoostOptimized { which, props }
  test->>wrapper: captureWrapper(os, jsxBody, preamble)
  wrapper-->>test: Capture { which, props }
  test->>diff: divergingKeys(normalize(boostProps), normalize(wrapperProps))
  diff-->>test: string[] of diverging keys
  test-->>fc: skipped | match | divergence

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• kuatsu/react-native-boost#23: Directly builds on the parity test helper infrastructure refactored here, including changes to captureBoost in boost.ts and the preamble/writeAndImportFresh flow.

Poem

🐇 Hop, hop, through the prop maze I go,
Fuzzing JSX with fast-check in tow!
canonical sorts, divergingKeys finds,
No parity bug shall escape these binds.
The rabbit runs tests—match, skip, diverge—
Each random case bends the optimizer's curve! 🎲

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 76.47% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'test: implement parity fuzzing' directly and clearly describes the main change—adding a comprehensive parity fuzzing test suite with property-based testing using fast-check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch test/parity-fuzzing

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/react-native-boost/src/plugin/__tests__/parity/fuzz/fuzz.test.ts`:
- Around line 89-101: The parity test property in fc.asyncProperty is failing on
a known divergence case where iOS with numberOfLines set to -1 produces
different results (boost.numberOfLines = -1 vs wrapper.numberOfLines = 0).
Before throwing the error when result.status === 'divergence', add a conditional
check to detect if this is the known ios plus numberOfLines negative value case
by examining the os parameter and spec properties, and if matched, increment a
quarantine counter and return early instead of throwing the error. This will
temporarily suppress the known divergence until the runtime clamp parity fix is
implemented.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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Configuration used: Organization UI

Review profile: CHILL

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Run ID: ea7292be-a952-45e0-babf-bc9166d7e3a1

📥 Commits

Reviewing files that changed from the base of the PR and between d012744 and d42af4c.

⛔ Files ignored due to path filters (1)

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (13)

• packages/react-native-boost/package.json
• packages/react-native-boost/src/plugin/__tests__/parity/boost.ts
• packages/react-native-boost/src/plugin/__tests__/parity/fuzz/diff.ts
• packages/react-native-boost/src/plugin/__tests__/parity/fuzz/fuzz.test.ts
• packages/react-native-boost/src/plugin/__tests__/parity/fuzz/generator.ts
• packages/react-native-boost/src/plugin/__tests__/parity/fuzz/vocabulary.ts
• packages/react-native-boost/src/plugin/__tests__/parity/generated.ts
• packages/react-native-boost/src/plugin/__tests__/parity/mocks/Platform.ts
• packages/react-native-boost/src/plugin/__tests__/parity/mocks/react-native.ts
• packages/react-native-boost/src/plugin/__tests__/parity/normalize.ts
• packages/react-native-boost/src/plugin/__tests__/parity/parity.test.ts
• packages/react-native-boost/src/plugin/__tests__/parity/vitest.config.parity.mts
• packages/react-native-boost/src/plugin/__tests__/parity/wrapper.ts