'Check Tree.id is correctly updated when the tree is copied after updated.'

def test_tree_copy_after_update(self):

    shas = []
    tree = Tree()
    shas.append(tree.id)
    tree.add('data', 420, Blob().id)
    copied = tree.copy()
    shas.append(tree.id)
    shas.append(copied.id)
    self.assertNotIn(shas[0], shas[1:])
    self.assertEqual(shas[1], shas[2])
