public void testCollection() {
SGFTree collection = new SGFTree();
int root1 = collection.newNode();
int root2 = collection.newNode();
collection.linkVariant(root1, root2);
assertEquals(SGFTree.ROOT, root1);
assertEquals(SGFTree.NULL, collection.getPrev(root1));
assertEquals(SGFTree.NULL, collection.getPrev(root2));
assertEquals(root2, collection.getNextVariant(root1));
}