def test_of_root(self):
t = Tree()
self.assertIsNone(t.next_leaf)
def test_of_last_leaf(self):
t = Tree()
t.add_child(Tree())
t.add_child(Tree())
self.assertIsNone(t.get_children()[1].next_leaf)
def test_4(self):
t = Tree()
t.add_child(Tree())
t.add_child(Tree())
t.get_children()[1].add_child(Tree())
self.assertEqual(t.get_children()[0].next_leaf,
t.get_children()[1].get_children()[0])
def test_1(self):
t = Tree()
self.assertIsNone(t.previous_leaf)
def test_3(self):
t = Tree()
t.add_child(Tree())
t.add_child(Tree())
self.assertEqual(t.get_children()[1].previous_leaf, t.get_children()[0])
def test_2(self):
t = Tree()
t.add_child(Tree())
t.add_child(Tree())
self.assertIsNone(t.get_children()[0].previous_leaf)
def test_1(self):
t = Tree()
self.assertIsNone(t.previous_sibling)