def test_erase2(self):
vars1 = Variables([x, y, z])
vars2 = Variables([w, z])
count = vars1.erase(vars2)
self.assertEqual(count, 1)
self.assertEqual(vars1.size(), 2)
def test_erase1(self):
vars = Variables([x, y, z])
count = vars.erase(x)
self.assertEqual(count, 1)
