def test_add_duplicate_town(self):
t = Town('Test Town')
s = State('Test State')
s._add_town(t)
with pytest.raises(ValueError) as verr:
s._add_town(t)
assert 'Town already exists' in str(verr.value)
def test_add_town(self):
t = Town('Test Town')
s = State('Test State')
s._add_town(t)
assert t in s.towns
