feat(WPTRunner): parse META tags

[KhafraDev]

• Allows parsing META tags and injecting individual scripts into each test. Example of META tags: https://github.com/web-platform-tests/wpt/blob/master/fetch/api/abort/general.any.js#L1-L5
• Runs each test in its own Worker.
• Throws an AbortError DOMException in the body mixin methods if the request has been aborted, rather than a TypeError. This behavior, albeit not mentioned in the spec, is tested for in the WPTs.
• Supports enabling flaky/expected failures for certain tests.
• Logs stats (# completed, # succeeded, # failed, etc.) once every test is completed.

[KhafraDev]

This test is failing and I'm not really sure how to fix it 😕

import { fetch, setGlobalOrigin } from 'undici'
import assert from 'assert'

setGlobalOrigin('http://localhost:3000')

const controller = new AbortController();
const signal = controller.signal;
controller.abort();

const log = [];

await Promise.all([
	fetch('../resources/data.json', { signal }).then(
		() => assert_unreached("Fetch must not resolve"),
		() => log.push('fetch-reject')
	),
	Promise.resolve().then(() => log.push('next-microtask'))
]);

assert.deepStrictEqual(log, ['fetch-reject', 'next-microtask']);

[codecov-commenter]

Codecov Report

Base: 94.89% // Head: 94.90% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (ce2c132) compared to base (9c3f34c).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1664      +/-   ##
==========================================
+ Coverage   94.89%   94.90%   +0.01%     
==========================================
  Files          53       53              
  Lines        4803     4813      +10     
==========================================
+ Hits         4558     4568      +10     
  Misses        245      245              

Impacted Files	Coverage Δ
lib/fetch/body.js	97.26% <100.00%> (+0.15%)	⬆️

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[mcollina]

lgtm

[KhafraDev]

The throwIfAborted steps in the body mixin methods aren't correct - there's a bug somewhere in undici I haven't managed to figure out just yet. However it could also be fixed in a separate pr as the workaround doesn't seem to cause issues.

edit: the issue is the order in which the promise is resolved/rejected. I don't know how to solve this without breaking the spec.

function createDeferredPromise () {
  let res
  let rej
  const promise = new Promise((resolve, reject) => {
    res = resolve
    rej = reject
  })

  return { promise, resolve: res, reject: rej }
}

async function fetch () {
  const promise = createDeferredPromise()

  queueMicrotask(() => promise.reject(new Error('AbortError')))

  promise.resolve()

  return promise.promise
}

await fetch() // resolves

[mcollina]

lgtm