def METHOD_NAME(self):
    clade_counts = {frozenset(['A', 'B']): 6,
                    frozenset(['A']): 7,
                    frozenset(['B']): 8}
    edge_lengths = {frozenset(['A', 'B']): 1,
                    frozenset(['A']): 2,
                    frozenset(['B']): 3}
    tree = _build_trees(clade_counts, edge_lengths, 'foo', TreeNode)[0]
    self.assertEqual(tree.foo, 6)
    tree_foos = set([c.foo for c in tree.children])
    tree_lens = set([c.length for c in tree.children])
    self.assertEqual(tree_foos, set([7, 8]))
    self.assertEqual(tree_lens, set([2, 3]))