SerializerExtension example

$runtime = new SerializerRuntime(new Serializer([new ObjectNormalizer($meta)], [new JsonEncoder(), new YamlEncoder()]));

        $mockRuntimeLoader = $this->createMock(RuntimeLoaderInterface::class);
        $mockRuntimeLoader
            ->method('load')
            ->willReturnMap([
                ['Symfony\Bridge\Twig\Extension\SerializerRuntime', $runtime],
            ])
        ;

        $twig = new Environment(new ArrayLoader(['template' => $template]));
        $twig->addExtension(new SerializerExtension());
        $twig->addRuntimeLoader($mockRuntimeLoader);

        return $twig;
    }
}