Phpunit doesn't recognize my project namespaces and class names - phpunit

Question

recently I've recognized that the project opis/closure is facing issues with deprecated serialization solution for php 8.1.1. So I created a fork of that and tried to fix the issue, while I was fixing the issue, I tried to test the output with the phpunit. but I've got some errors shown bellow. can you please check and feed me back about how to solve these issues:
Title
Description
Operating system
macintosh
PHP version:
PHP 8.1.1 (cli) (built: Dec 17 2021 23:49:52) (NTS) Copyright (c) The PHP Group Zend Engine v4.1.1, Copyright (c) Zend Technologies
PHP Unit version:
PHPUnit 9.5.10 by Sebastian Bergmann and contributors.
Project Git repo:
https://github.com/rhashnull/closure (my fork)
The error message:
PHP Fatal error: Uncaught Error: Class "Opis\Closure\SerializableClosure" not found in /<private_path>/Projects/closure/tests/ClosureTest.php:447
Stack trace:
#0 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/Util/FileLoader.php(56): include_once()
#1 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/Util/FileLoader.php(43): PHPUnit\Util\FileLoader::load('/Users/arash/Pr...')
#2 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/Framework/TestSuite.php(311): PHPUnit\Util\FileLoader::checkAndLoad('/Users/arash/Pr...')
#3 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/Framework/TestSuite.php(394): PHPUnit\Framework\TestSuite->addTestFile('/Users/arash/Pr...')
#4 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/Runner/BaseTestRunner.php(85): PHPUnit\Framework\TestSuite->addTestFiles(Array)
#5 phar:///usr/local/Cellar/phpunit/9.5.10/bin/phpunit/phpunit/TextUI/Command.php(108): PHPUnit\Runner\BaseTestRunner->getTest('/Users/arash/Pr...', Array)
phpunit.xml
<phpunit bootstrap="./vendor/autoload.php" verbose="true">
<testsuites>
<testsuite name="Main">
<file phpVersion="5.4.0" phpVersionOperator=">=">./tests/ClosureTest.php</file>
</testsuite>
<testsuite name="Serialize">
<file phpVersion="5.4.0" phpVersionOperator=">=">./tests/SerializeTest.php</file>
</testsuite>
<testsuite name="Recursive">
<file phpVersion="7.1.0" phpVersionOperator="<">./tests/RecursiveArrayTest.php</file>
</testsuite>
<testsuite name="Signed">
<file phpVersion="5.4.0" phpVersionOperator=">=">./tests/SignedClosureTest.php</file>
</testsuite>
<testsuite name="Namespace">
<file phpVersion="5.5.0" phpVersionOperator=">=">./tests/NamespaceTest.php</file>
<file phpVersion="5.5.0" phpVersionOperator=">=">./tests/NamespaceUnqualifiedTest.php</file>
<file phpVersion="5.5.0" phpVersionOperator=">=">./tests/NamespaceFullyQualifiedTest.php</file>
<file phpVersion="5.5.0" phpVersionOperator=">=">./tests/NamespacePartiallyQualifiedTest.php</file>
</testsuite>
<testsuite name="ReflectionClosure">
<file phpVersion="5.4.0" phpVersionOperator=">=">./tests/ReflectionClosureTest.php</file>
</testsuite>
<testsuite name="ReflectionClosure2">
<file phpVersion="7.0.0" phpVersionOperator=">=">./tests/ReflectionClosure2Test.php</file>
</testsuite>
<testsuite name="ReflectionClosure3">
<file phpVersion="7.1.0" phpVersionOperator=">=">./tests/ReflectionClosure3Test.php</file>
</testsuite>
<testsuite name="ReflectionClosure4">
<file phpVersion="7.2.0" phpVersionOperator=">=">./tests/ReflectionClosure4Test.php</file>
</testsuite>
<testsuite name="ReflectionClosure5">
<file phpVersion="7.4.0" phpVersionOperator=">=">./tests/ReflectionClosure5Test.php</file>
<file phpVersion="7.4.0" phpVersionOperator=">=">./tests/NamespaceGroupTest.php</file>
</testsuite>
<testsuite name="ReflectionClosure6">
<file phpVersion="8.0.0-dev" phpVersionOperator=">=">./tests/ReflectionClosure6Test.php</file>
</testsuite>
</testsuites>
</phpunit>
composer.json
{
"name": "opis/closure",
"description": "A library that can be used to serialize closures (anonymous functions) and arbitrary objects.",
"keywords": ["closure", "serialization", "function", "serializable", "serialize", "anonymous functions"],
"homepage": "https://opis.io/closure",
"license": "MIT",
"authors": [
{
"name": "Marius Sarca",
"email": "marius.sarca#gmail.com"
},
{
"name": "Sorin Sarca",
"email": "sarca_sorin#hotmail.com"
}
],
"require": {
"php": "^5.4 || ^7.0 || ^8.0"
},
"require-dev": {
"jeremeamia/superclosure": "^2.0",
"phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0 || ^8.0 || ^9.0"
},
"autoload": {
"psr-4": {
"Opis\\Closure\\": "src/"
},
"files": ["functions.php"]
},
"autoload-dev": {
"psr-4": {
"Opis\\Closure\\Test\\": "tests/"
}
},
"extra": {
"branch-alias": {
"dev-master": "3.6.x-dev"
}
},
"config": {
"preferred-install": "dist",
"sort-packages": true
}
}
Special thanks to your attention.