Testing properties that are date-related

[Tim Chase]

Are there best practices for testing dates that are properties 
which take the current date into consideration?  I have something 
like

   class Foo:
     def _get_year_range(self):
       return (self._min_year, self._max_year)
     def _set_year_range(self, year):
       if isinstance(year, tuple):
         _min, _max = map(window_date, year)
         if _min > _max: _min, _max = _max, _min
       else: # a raw int
         _min = _max = window_date(year)
       self._min_year, self._max_year = _min, _max
     year_range = property(
       fget=_get_year_range,
       fget=_get_year_range,
       )

The problem is that the behavior of the window_date function 
depends on the current date (the function makes a guess about 
adding the century if the year was <100).  It *does* take an 
"around" parameter that defaults to the current date.  So for 
pure testing of the window_date() function, I can hard-code some 
date where I know what the expected values should be.

However if I want to write a test-harness for my property, I have 
no way (AFAIK) to pass in this fixed date to _set_year_range() so 
that the success/failure of my tests doesn't depend on the day I 
run them:

   class TestFoo:
     def test_year_range(self):
       around = date(2011,1,1)
       f = Foo()
       f.year_range = (97, 84)
       self.assertEqual(f.year_range, (1984, 1997))

Any suggestions/tips/hints?  Thanks,

-tkc