SF functional test example

FunctionTest.php

public function testSomething(): void
{
    $client = static::createClient();
    
    $entity = self::$container->get('em')->find(…, 1);
    $entity->setState(1);
    self::$container->get('em')->persist($entity);
    self::$container->get('em')->flush();
    
    $client->request(…, …);
    
    $entity->setState(2);
    self::$container->get('em')->persist($entity);
    self::$container->get('em')->persist($entity);
    // Boom
    self::$container->get('em')->flush();
}

ServiceResetter during Kernel boot will clear the EM no matter what, so not too much one can do