composer.json

{
    "name": "tomjn/composer-webtest",
    "description": "tests for web based composer uis",
    "license": "GPL-V2.0",
    "authors": [
        {
            "name": "Tom J Nowell",
            "email": "contact@tomjn.com"
        }
    ],
    "minimum-stability": "dev",
    "require": {
        "composer/composer": "*"
    }
}

index.php

<?php

use Composer\IO\NullIO;
use Composer\Installer;
use Composer\Plugin\CommandEvent;
use Composer\Plugin\PluginEvents;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Input\InputOption;
use Symfony\Component\Console\Input\InputArgument;
use Symfony\Component\Console\Input\StringInput;
use Symfony\Component\Console\Output\NullOutput;
use Symfony\Component\Console\Output\OutputInterface;

if ( file_exists( 'vendor/autoload.php' ) ) {
	require 'vendor/autoload.php';
} else {
	echo '<p>You must run composer install on this folder for the needed dependencies</p>';
}

echo '<p>hello there, there should be a test folder with a composer.json in it. This script will change into that directory and attempt a composer install</p>';

chdir( 'test' );

// a lot of this was taken from the install command
$factory = new Composer\Factory();
$io = new NullIO();
$composer = $factory->createComposer( $io );

$composer->getDownloadManager()->setOutputProgress( false );

$output = new NullOutput();
$input = new StringInput( '' );

$commandEvent = new CommandEvent( PluginEvents::COMMAND, 'install', $input, $output );
$composer->getEventDispatcher()->dispatch( $commandEvent->getName(), $commandEvent );

$install = Installer::create( $io, $composer );

$preferSource = false;
$preferDist = false;

$config = $composer->getConfig();

switch ($config->get('preferred-install')) {
	case 'source':
		$preferSource = true;
		break;
	case 'dist':
		$preferDist = true;
		break;
	case 'auto':
	default:
		// noop
		break;
}

$optimize = $config->get('optimize-autoloader');

$install
	->setDryRun( false)
	->setVerbose( false )
	->setPreferSource( false )
	->setPreferDist( true )
	->setDevMode( false)
	->setRunScripts( false )
	->setOptimizeAutoloader( $optimize )
;


echo '<p>Created and configured composer objects, running install</p>';
$result = $install->run();

echo '<p>Installer ran, and returned with value: <code>'.print_r( $result, true ).'</code></p>';