If I were testing the initialisation of `class TimeConstraint`, I would also test a successful result also.  Since your defining a subclass of the `Constraint` object, I would have an `assertIs` test for the two attributes `self._hour` and `self._coord` on the resulting `TimeConstraint` object.  Changing the design of the `Constraint` object could conceivably override these attributes and then it go unnoticed.

Example:

```Python
>>> class A(object):
...     def __init__(self, a='tree'):
...         self.a = a
... 
>>> class B(A):
...     def __init__(self, a='apple'):
...         self.a = a
...         super(B, self).__init__()
... 
>>> foo = B()
>>> foo.a
'tree'
```