def test_diff(self):
e1 = Environment(a=1, b=2, c=3, d=4, e=5)
e2 = Environment(a=0, b=1, d=3, f=6, g=7)
d = e2.diff(e1)
self.assertEqual(d.added, [('f', 6), ('g', 7)])
self.assertEqual(d.modified, [('a', 1, 0), ('b', 2, 1), ('d', 4, 3)])
self.assertEqual(d.removed, [('c', 3), ('e', 5)])
