def test_compare_energy(self):
a = Nibble('a', self.world)
b = Nibble('b', self.world)
assert_equal(a.compare_energy(b), 0)
a.move(1,1)
assert_equal(a.compare_energy(b), -1)
b.move(2,2)
assert_equal(a.compare_energy(b), 1)
