then-httplug.php

<?php

require __DIR__ . "/vendor/autoload.php";

use Amp\Promise;

$client = new Http\Adapter\Artax\Client;

$request1 = new GuzzleHttp\Psr7\Request("GET", "http://example.com/");

print $client->sendAsyncRequest($request1)
    ->then(function ($response) {
        return $response->withStatus(523);
    })
    ->wait()->getStatusCode() . PHP_EOL;

Try:

<?php
require __DIR__ . "/vendor/autoload.php";
use Amp\Promise;
$client = new Http\Adapter\Artax\Client;
$request1 = new GuzzleHttp\Psr7\Request("GET", "http://example.com/");
var_dump(
    $client->sendAsyncRequest($request1)
        ->then(function ($response) {
            return $response->getBody()->__toString();
        })
        ->wait()

Apart from a missing );, yeah.

PHP Fatal error:  Uncaught Http\Client\Exception\TransferException: Bad reponse returned in /home/kelunik/GitHub/php-http/artax-adapter/src/Internal/Promise.php:50

But just looked at the interface, seems like it doesn't have to behave like that and we could fix it?