Did you experience any nasty side effect of this not being reset? Can you add a corresponding test case?

Did you experience any nasty side effect of this not being reset?

IMHO it should only have a minimum performance impact, because the name is resolved for every test:

It could have a performance impact. That's why I'm asking. Why do you want to reset this property, if everything is fine when it is not reset?

I have some projects that will perform web tests with different kernel configuration. This can also be the case, if you provide a bundle with optional dependencies that will result in a slightly different service configuration.

At the moment, I have to manuell reset the ::$class after every test with a local tearDown method. When I don't do this, the first (randomly selected) test will reserve the kernel class and all other test will fail, because they expect a different kernel class.

Thank you @core23.

This currently is now breaking in our cases the tests as we are defining the static::$class once at the top of the testcases: https://github.com/sulu/sulu/blob/b45f91ff36b468d200b254f894368cb0c3380671/src/Sulu/Bundle/MediaBundle/Tests/Functional/Media/Storage/S3StorageTest.php#L22

And now as it is set to null on teardown all tests after the first tests are failing.

Can this be related?
After update 6.0.3->6.0.5

LogicException : Could not find service "test.service_container". Try updating the "framework.test" config to "true".
 /var/www/symfony/vendor/symfony/framework-bundle/Test/KernelTestCase.php:98
 /var/www/symfony/tests/Controller/DefaultControllerTest.php:70
 
 Caused by
 Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: The "kernel" service is synthetic, it needs to be set at boot time before it can be used.

I have already framework.test=true.

@mwalczak nope, see #45580 for this issue.

I could workaround my issue by changing:

-    protected static $class = S3Kernel::class;

+    protected static function getKernelClass(): string
+    {
+        return S3Kernel::class;
+    }

EDIT: for prefer lowest tests I had to readd the static $class so now both is required in our case:

+    protected static $class = S3Kernel::class;
+
+    protected static function getKernelClass(): string
+    {
+        return S3Kernel::class;
+    }