PHPUnit's error handler is not registered if Symfony is booted in a "before class" hook

[nikophil]

Q	A
PHPUnit version	>= 10
PHP version	8.3 (any)
Installation Method	Composer

Summary

Hi,

When using Symfony, if the kernel is booted in a "before class" hook, deprecations are not handled by PHPUnit's error handler. Actually, PHPUnit's error handler is not enabled at all, because another error handler is already registered.

I'm trying to open an issue here, to see if it would possible to mitigate the problem in PHPUnit?

Current behavior

Deprecation, for instance are not shown in PHPUnit's output.

How to reproduce

final class SomeTest extends KernelTestCase
{
    public static function setUpBeforeClass(): void
    {
        self::bootKernel(); // <== if this line is removed, the deprecation is displayed
    }

    public function testWithDeprecation(): void
    {
        @trigger_error('some deprecation', \E_USER_DEPRECATED);
        self::assertTrue(true);
    }
}

thanks!