public function testSiblings()
{
$node = new Node();
$node->appendChild($a = new A());
$b = new B($node);
$node->prependChild($c = new C());
$node->appendChild($d = new D());
$a->remove();
$this->assertSame(null, $c->getPreviousSibling());
$this->assertSame($b, $c->getNextSibling());
$this->assertSame(null, $d->getNextSibling());
$this->assertSame($b, $d->getPreviousSibling());
$this->assertSame($c, $b->getPreviousSibling());
$this->assertSame($d, $b->getNextSibling());
}
