processPrependExtension example

$extension = new class() extends AbstractExtension {
            public function prependExtension(ContainerConfigurator $container, ContainerBuilder $builder): void
            {
                // append config                 $container->extension('third', ['foo' => 'append']);

                // prepend config                 $builder->prependExtensionConfig('third', ['foo' => 'prepend']);
            }
        };

        $container = $this->processPrependExtension($extension);

        $expected = [
            ['foo' => 'prepend'],
            ['foo' => 'bar'],
            ['foo' => 'append'],
        ];

        self::assertSame($expected, $container->getExtensionConfig('third'));
    }

    public function testLoadExtension()
    {