hacklang async?

asynctest.php

<?hh //partial

class TestResult {

    public function __construct(public string $message)
    {
    }
}

class TestCase {

    public function __construct(protected string $name)
    {
    }

    public function testSlower(): TestResult
    {
        $i = 0;
        while ($i < 1000000000) {
            $i++;
        }
        return new TestResult("test slower OK\n");
    }

    public function testFaster(): TestResult
    {
        $i = 0;
        while ($i < 100000) {
            $i++;
        }
        return new TestResult("test faster OK\n");
    }

    public function run(): TestResult
    {
        if ($this->name == "testSlower") {
            $result = $this->testSlower();
        } else {
            $result = $this->testFaster();
        }
        print $result->message;
        return $result;
    }
}

$testSlower = new TestCase('testSlower');
$testFaster = new TestCase('testFaster');

async function runTest(TestCase $case): Awaitable<TestResult> {
    //how can I make this run in parallel?
    return $case->run();
}

async function runTests(array<TestCase> $cases): Awaitable<T> {
    $tasks = array();
    foreach ($cases as $case) {
        $tasks[] = runTest($case);
    }
    await GenArrayWaitHandle::create($tasks);
}

runTests(array($testSlower, $testFaster))->join();//expect testFaster to execute first