def test_is_valid(self):
goal = Goal("New Goal")
self.assertTrue(goal.is_valid())
goal.add_neighbor(Variable("New Variable"), Constraint([]))
self.assertFalse(goal.is_valid())
goal = Goal("New Goal")
constraint = Constraint([[Equals(3)]])
variable = Variable("New Variable", 5)
goal.add_neighbor(variable, constraint)
self.assertFalse(goal.is_valid())
