verride the __init__ method, the base class
    __init__ method must always be called. It is important that subclasses
    should not change the signature of their __init__ method, since instances
    of the classes are instantiated automatically by parts of the framework
    in order to be run.

    When subclassing TestCase, you can set these attributes:
    * failureException: determines which exception will be raised when
        the instance's assertion methods fail; test methods raising this
        exception will be deemed to have 'failed' rather than 'errored'.
    * longMessage: determines whether long messages (including repr of
        objects used in assert methods) will be printed on failure in *addition*
        to any explicit message passed.
    * maxDiff: sets the maximum length of a diff in failure messages
        by assert methods using difflib. It is looked up as an instance
        attribute so can be configured by individual tests if required.
    Ti€