expectUserDeprecationMessage*() fails when test is run in separate process

[mondrake]

Q	A
PHPUnit version	11.5.2
PHP version	8.3.9
Installation Method	Composer

Summary

expectUserDeprecationMessage*() fails when test is run in separate process.

Current behavior

A test like this

<?php

declare(strict_types=1);

use PHPUnit\Framework\TestCase;
use PHPUnit\Framework\Attributes\RunInSeparateProcess;

class ExpectDeprecationTest extends TestCase {

  /**
   * Tests expectDeprecation.
   */
  public function testExpectDeprecation(): void {
    $this->expectUserDeprecationMessage('Test deprecation');
    @trigger_error('Test deprecation', E_USER_DEPRECATED);
  }

  /**
   * Tests expectDeprecation in isolated test.
   */
  #[RunInSeparateProcess]
  public function testExpectDeprecationInIsolation(): void {
    $this->expectUserDeprecationMessage('Test isolated deprecation');
    @trigger_error('Test isolated deprecation', E_USER_DEPRECATED);
  }

}

leads to an EventFacadeIsSealedException error reported by the runner:

PHPUnit 11.5.2 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.3.9
Configuration: /Users/xxx/Dev/drupal/core/phpunit.xml.dist

DE                                                                  2 / 2 (100%)

Time: 00:01.879, Memory: 14.00 MB

There was 1 error:

1) ExpectDeprecationTest::testExpectDeprecationInIsolation
PHPUnit\Event\EventFacadeIsSealedException:

--

2 tests triggered 2 deprecations:

1) /Users/xxx/Dev/drupal/core/tests/Drupal/Tests/ExpectDeprecationTest.php:15
Test deprecation

2) /Users/xxx/Dev/drupal/core/tests/Drupal/Tests/ExpectDeprecationTest.php:24
Test isolated deprecation

ERRORS!
Tests: 2, Assertions: 2, Errors: 1, Deprecations: 2.

How to reproduce

See above

Expected behavior

No exception reported, only the deprecations.