DummyExtension example

private ExtensionCompilerPass $pass;

    protected function setUp(): void
    {
        $this->container = new ContainerBuilder();
        $this->pass = new ExtensionCompilerPass();
    }

    public function testProcess()
    {
        $extension1 = new CompilerPassExtension('extension1');
        $extension2 = new DummyExtension('extension2');
        $extension3 = new DummyExtension('extension3');
        $extension4 = new CompilerPassExtension('extension4');

        $this->container->registerExtension($extension1);
        $this->container->registerExtension($extension2);
        $this->container->registerExtension($extension3);
        $this->container->registerExtension($extension4);

        $this->pass->process($this->container);

        $this->assertTrue($this->container->hasDefinition('extension1'));