Test262 test harness and initial pass rate #105

Set up the Test262 test harness integration and measure initial pass rate.

Scope#

Test262 Submodule#

• The Test262 suite is already a git submodule at tests/test262/
• Contains thousands of tests for ECMAScript conformance
• Tests use a standard harness ($262, assert, assert.sameValue, etc.)

Test Harness#

• Implement the Test262 harness helpers that tests depend on:
  • assert(condition, message) — throw if falsy
  • assert.sameValue(actual, expected, message) — SameValue comparison
  • assert.notSameValue(actual, expected, message)
  • assert.throws(expectedError, fn, message) — verify fn throws expected error type
  • $262.createRealm() (basic — can return a fresh global)
  • $262.gc() — trigger GC
  • print() / $DONE() for async tests
• Test runner that:
  • Discovers test files matching a pattern
  • Reads test metadata (frontmatter: features, flags, negative)
  • Skips tests requiring unimplemented features
  • Executes each test in a fresh realm
  • Reports pass/fail/skip/error
  • Handles negative tests (expected parse or runtime errors)
  • Handles async tests ($DONE callback)

Integration#

• cargo test -p we-js should run a curated subset of Test262
• Focus on core language tests first:
  • test/language/expressions/
  • test/language/statements/
  • test/language/types/
  • test/built-ins/Object/ (basic subset)
  • test/built-ins/Array/ (basic subset)
  • test/built-ins/String/ (basic subset)
• Track pass rate (e.g., X/Y tests passing)
• Tests that require unimplemented features should be skipped, not fail

Acceptance Criteria#

• Test runner discovers and executes Test262 tests
• Harness helpers (assert, assert.sameValue, assert.throws) work
• Negative tests (expected errors) handled correctly
• Test metadata parsing (frontmatter features and flags)
• Feature-based test skipping for unimplemented features
• Pass rate tracking with summary output
• At least basic expression and statement tests pass
• Integration with cargo test -p we-js

Phase 10 — JavaScript Engine (issue 15b of 15). Depends on: All previous Phase 10 issues.