Test262 Harness Integration

This directory contains the WPT-specific infrastructure for running the TC39 Test262 suite within the Web Platform Tests framework.

Overview

Test262 tests are integrated into WPT using a “Window Wrapper” pattern. Each Test262 .js test is served as a .test262.html file that wraps the actual test execution in an isolated environment.

Architecture

1. Top-Level Wrapper: A standard WPT HTML file (testharness.js-enabled) that contains an <iframe> where the actual test code runs. It defines a global hook window.test262HarnessDone to receive results. It maps Test262 results to a single WPT async_test.
2. Test Iframe: The environment where the Test262 test executes. It includes:
   • Harness Files: Required Test262 harness files (e.g., assert.js, sta.js) from third_party/test262/harness/.
   • Provider (test262-provider.js): Implements the $262 host API required by the spec.
   • Reporter (test262-reporter.js): Captures errors, handles async signals, and communicates with the parent window.

Core Protocol (INTERPRETING.md)

This implementation strictly follows the Test262 INTERPRETING.md specification:

Success and Failure

• A test passes if it completes its execution without throwing an uncaught exception.
• A test fails if it throws a Test262Error.
• Any other uncaught exception is reported as a harness ERROR.

Asynchronous Tests (async flag)

Tests tagged with async must signal completion via the host-defined print() function:

• print('Test262:AsyncTestComplete') -> PASS
• print('Test262:AsyncTestFailure: [reason]') -> FAIL

The $262.done() (or $DONE()) helper is wired to this print() protocol.

Negative Tests (negative flag)

Tests expecting an error are validated against their target type and phase. If such a test completes without throwing the expected error, it is reported as a failure.

Advanced Features

Strict Mode (onlyStrict flag)

Tests with the onlyStrict flag are served with a "use strict"; preamble or within a strict script context as required by the spec.

Modules (module flag)

Test262 module tests are served as <script type="module">. The runner uses dynamic import() to execute the test and handles completion once the module's top-level evaluation (and any async work) resolves.

Realms and Agents

• $262.createRealm(): Supported via sub-iframes.
• $262.agent: Supported via Web Workers and SharedArrayBuffer for multi-threaded tests.

Communication Protocol

The test executes in the iframe and reports results back to the parent window by calling window.parent.test262HarnessDone(status, message). The status values are mapped as follows:

• 0: OK (Success)
• 1: FAIL (Mapped to assert_unreached(message))
• 2: ERROR (Mapped to a harness error and re-thrown)