public function testAddExtension() {
$twig = new Twig_Environment(new Twig_Loader_String());
$twig
->addExtension(new Twig_Tests_EnvironmentTest_Extension());
$this
->assertArrayHasKey('test', $twig
->getTags());
$this
->assertArrayHasKey('foo_filter', $twig
->getFilters());
$this
->assertArrayHasKey('foo_function', $twig
->getFunctions());
$this
->assertArrayHasKey('foo_test', $twig
->getTests());
$this
->assertArrayHasKey('foo_unary', $twig
->getUnaryOperators());
$this
->assertArrayHasKey('foo_binary', $twig
->getBinaryOperators());
$this
->assertArrayHasKey('foo_global', $twig
->getGlobals());
$visitors = $twig
->getNodeVisitors();
$this
->assertEquals('Twig_Tests_EnvironmentTest_NodeVisitor', get_class($visitors[2]));
}