'The highest context is used if the given key isn\'t found.'

def test_set_upward_with_push_no_match(self):

    c = Context({'b': 1})
    c.push({'b': 2})
    c.set_upward('a', 2)
    self.assertEqual(len(c.dicts), 3)
    self.assertEqual(c.dicts[(-1)]['a'], 2)
