ObjectId t3 = id("a3");
ObjectId t4 = id("a4");
ObjectId t5 = id("a5");
ObjectId t6 = id("a6");
NodeRef r1 = tree("roads", t1, ObjectId.NULL);
NodeRef r11 = tree("roads/highways", t2, md1);
NodeRef r12 = tree("roads/streets", t3, md2);
NodeRef r2 = tree("buildings", t4, ObjectId.NULL);
NodeRef r21 = tree("buildings/stores", t5, md3);
NodeRef r22 = tree("buildings/unknown", t6, md4);
ImmutableList<NodeRef> refs = ImmutableList.of(r1, r11, r12, r2, r21, r22);
root = MutableTree.createFromRefs(id("abc"), refs.iterator());
assertNotNull(root);
}