public void RemoveSuccessorTest()
{
Node <City> ct = new Node <City> (new City("war", "maz", "24351"));
Node <City> r = n.AddSuccessor(ct);
Assert.True(n.RemoveSuccesor(ct));
Assert.False(n.successors.Contains(ct));
Assert.False(ct.predecessors.Contains(n));
Assert.False(r.successors.Contains(ct));
Assert.AreSame(n, r);
}