Symfony\Component\DependencyInjection\ContainerBuilder::registerExtension PHP Method

    public function registerExtension(ExtensionInterface $extension)
    {
        $this->extensions[$extension->getAlias()] = $extension;

        if (false !== $extension->getNamespace()) {
            $this->extensionsByNs[$extension->getNamespace()] = $extension;
        }
    }

 protected function setUp()
 {
     $this->extension = new GGTeamBreadcrumbExtension();
     $this->container = new ContainerBuilder();
     $this->container->registerExtension($this->extension);
     $this->container->set('templating', $this->getMockTemplatingEngine());
 }