Can't run SINGLE test files with namespace in class name

[jtowe1]

Q	A
PHPUnit version	9.5.9
PHP version	7.4.23
Installation Method	Composer

Summary

Our app has a mix of real namespaces and an older way of namespacing using underscores. Example, the path to this file is tests/Thing/ThingTest.php

<?php

class Thing_ThingTest extends PHPUnit\Framework\TestCase
{
    public function testThisThing()
    {
        $this->assertTrue(true);
    }
}

Current behavior

In phpunit 9.5.9 this happens when trying to run this test by its path.

deploy/vendor/bin/phpunit ./tests/Thing/ThingTest.php 
Class 'ThingTest' could not be found in '/home/me/project_folder/deploy/tests/Thing/ThingTest.php'.

But in phpunit 8.5.22 it works

deploy/vendor/bin/phpunit ./tests/Thing/ThingTest.php 
PHPUnit 8.5.22 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.4.23 with Xdebug 3.0.3
Configuration: /home/me/project_folder/phpunit.xml.dist

.                                                                   1 / 1 (100%)

Time: 740 ms, Memory: 32.00 MB

OK (1 test, 1 assertion)

How to reproduce

mkdir phpunit_test
cd phpunit_test
composer require phpunit/phpunit:^9.5 --dev
mkdir Thing

Edit composer.json to look like this

{
    "autoload-dev": {
        "psr-0": {
            "": "./"
        }
    },
    "require-dev": {
        "phpunit/phpunit": "^9.5"
    }
}

Create Thing/ThingTest.php

<?php

class Thing_ThingTest extends PHPUnit\Framework\TestCase
{
    public function testThisThing()
    {
        $this->assertTrue(true);
    }
}

Run the test

vendor/bin/phpunit Thing/ThingTest.php
Class 'ThingTest' could not be found in '/Users/jtowe/Documents/Projects/phpunit_test/Thing/ThingTest.php'.

Revert back to 8.5 and see that it works

composer require phpunit/phpunit:^8.5 --dev -W
vendor/bin/phpunit Thing/ThingTest.php
PHPUnit 8.5.22 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 14 ms, Memory: 4.00 MB

OK (1 test, 1 assertion)

NOTE: This only seems to happen when I try to run the test by itself. If I make a phpunit.xml of

<?xml version="1.0" encoding="UTF-8"?>
<phpunit
    bootstrap="./vendor/autoload.php"
    >
    <testsuites>
        <testsuite name="Test Suite">
            <directory>./</directory>
        </testsuite>
    </testsuites>
</phpunit>

And run all the tests vendor/bin/phpunit it works

PHPUnit 9.5.11 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 00:00.001, Memory: 6.00 MB

OK (1 test, 1 assertion)

Expected behavior

I'm not sure what's happening but there's a high chance i'm just doing something wrong. We have LOTS of tests namespaced using underscores so if the answer is to namespace them all using Namespace I may have to revert back to 8.5 for now. I think i'd just like to understand what's changed to make this happen so I can revert or fix it.

composer info | sort

composer info | sort                                                                                     1 ✘  12:55:47 PM 
doctrine/instantiator              1.4.0   A small, lightweight utility to instantiate objects in PHP without invoking their constructors
myclabs/deep-copy                  1.10.2  Create deep copies (clones) of your objects
nikic/php-parser                   v4.13.2 A PHP parser written in PHP
phar-io/manifest                   2.0.3   Component for reading phar.io manifest information from a PHP Archive (PHAR)
phar-io/version                    3.1.0   Library for handling version information and constraints
phpdocumentor/reflection-common    2.2.0   Common reflection classes used by phpdocumentor to reflect the code structure
phpdocumentor/reflection-docblock  5.3.0   With this component, a library can provide support for annotations via DocBlocks or otherwise retrieve information that ...
phpdocumentor/type-resolver        1.6.0   A PSR-5 based resolver of Class names, Types and Structural Element Names
phpspec/prophecy                   v1.15.0 Highly opinionated mocking framework for PHP 5.3+
phpunit/php-code-coverage          9.2.10  Library that provides collection, processing, and rendering functionality for PHP code coverage information.
phpunit/php-file-iterator          3.0.6   FilterIterator implementation that filters files based on a list of suffixes.
phpunit/php-invoker                3.1.1   Invoke callables with a timeout
phpunit/php-text-template          2.0.4   Simple template engine.
phpunit/php-timer                  5.0.3   Utility class for timing
phpunit/phpunit                    9.5.11  The PHP Unit Testing framework.
sebastian/cli-parser               1.0.1   Library for parsing CLI options
sebastian/code-unit                1.0.8   Collection of value objects that represent the PHP code units
sebastian/code-unit-reverse-lookup 2.0.3   Looks up which function or method a line of code belongs to
sebastian/comparator               4.0.6   Provides the functionality to compare PHP values for equality
sebastian/complexity               2.0.2   Library for calculating the complexity of PHP code units
sebastian/diff                     4.0.4   Diff implementation
sebastian/environment              5.1.3   Provides functionality to handle HHVM/PHP environments
sebastian/exporter                 4.0.4   Provides the functionality to export PHP variables for visualization
sebastian/global-state             5.0.3   Snapshotting of global state
sebastian/lines-of-code            1.0.3   Library for counting the lines of code in PHP source code
sebastian/object-enumerator        4.0.4   Traverses array structures and object graphs to enumerate all referenced objects
sebastian/object-reflector         2.0.4   Allows reflection of object attributes, including inherited and non-public ones
sebastian/recursion-context        4.0.4   Provides functionality to recursively process PHP variables
sebastian/resource-operations      3.0.3   Provides a list of PHP built-in functions that operate on resources
sebastian/type                     2.3.4   Collection of value objects that represent the types of the PHP type system
sebastian/version                  3.0.2   Library that helps with managing the version number of Git-hosted PHP projects
symfony/polyfill-ctype             v1.24.0 Symfony polyfill for ctype functions
theseer/tokenizer                  1.2.1   A small library for converting tokenized PHP source code into XML and potentially other formats
webmozart/assert                   1.10.0  Assertions to validate method input/output with nice error messages.

[jtowe1]

Tested again in 9.5.20 and it still happens.

[chiragkalani]

Tested in 9.5.21 and it still happens.

[sebastianbergmann]

This should have been fixed by #5021.