@runTestsInSeparateProcesses results in infinite loop when installed with Composer ^2.2

[rdarcy1]

Q	A
PHPUnit version	9.5.10
PHP version	8.0.13
Installation Method	Composer 2.2.0, 2.21

Summary

After composer install with composer 2.2.0 or 2.2.1, running a PHPUnit test with separate process flag results in an infinite loop. Possibly related to #4835?

Apologies if this is an issue with Composer rather than PHPUnit. I know there were a few reported issues with the Composer 2.2.0 release, but I think they've been marked resolved with the 2.2.1 patch? E.g. composer/composer#10387

Current behavior

PHPUnit appears to keep spawning new child processes. Keeps looping and consuming memory until terminated.

How to reproduce

Ensure no vendor directory exists.
Install composer 2.2.0 or 2.2.1 and composer install:

curl -sS https://getcomposer.org/installer | php -- --filename=composer --version=2.2.1
./composer install

composer.json:

{
    "name": "robin/phpunit_separate_process_test",
    "require-dev": {
        "phpunit/phpunit": "^9.0"
    }
}

MyTest.php

<?php

use PHPUnit\Framework\TestCase;

/** @runTestsInSeparateProcesses */
class MyTest extends TestCase
{
    /** @test */
    public function aTest()
    {
        $this->assertTrue(true);
    }
}

phpunit.xml (created using --generate-configuration)

<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
         bootstrap="vendor/autoload.php"
         cacheResultFile=".phpunit.cache/test-results"
         executionOrder="depends,defects"
         forceCoversAnnotation="true"
         beStrictAboutCoversAnnotation="true"
         beStrictAboutOutputDuringTests="true"
         beStrictAboutTodoAnnotatedTests="true"
         convertDeprecationsToExceptions="true"
         failOnRisky="true"
         failOnWarning="true"
         verbose="true">
    <testsuites>
        <testsuite name="default">
            <directory>tests</directory>
        </testsuite>
    </testsuites>
</phpunit>

Run tests:

vendor/bin/phpunit --debug

Expected behavior

Tests should run to completion (as is the case with composer 2.1.14).

[sebastianbergmann]

@Seldaek Is this fixed by #4846?

[Seldaek]

If using the latest composer snapshot (composer selfupdate --snapshot) then removing vendor/bin/phpunit and running composer install fixes it then yes most likely it's fixed by #4846

[rdarcy1]

Can confirm it's fixed for me with composer selfupdate --snapshot. Sorry didn't see your PR, thanks for the speedy fix.