I'm not exactly sure what he meant either. But I propose to add:
```python
class Test___init__(tests.IrisTest):
    def test_default(self):
        constraint = TimeConstraint()
        self.assertIsNone(constraint.hour)
        self.assertEqual(constraint.coord, 'time')

    def test_explicit(self):
        constraint = TimeConstraint(hour=4, coord='quee')
        self.assertEqual(constraint.hour, 4)
        self.assertEqual(constraint.coord, 'quee')
```
Which tests the results of construction via the *public* interface.