from datetime import date
import unittest


def calculate_age(birth_date, until=None):
    """
    Calculates the age of a person from their birth date to a given
    date, accounting for birth dates during leap year.  The date
    defaults to today if no date is specified.
    """
    until = until or date.today()

    try:
        birthday = date(until.year, birth_date.month, birth_date.day)
    except ValueError:
        birthday = date(until.year, birth_date.month, birth_date.day - 1)

    if birthday > until:
        return until.year - birth_date.year - 1
    else:
        return until.year - birth_date.year


class CalculateAgeTest(unittest.TestCase):

    def test_calculate_age(self):
        data = [
            # test normal dates
            [
                date(year=1982, month=11, day=26),
                date(year=2000, month=11, day=25),
                17,
            ],
            [
                date(year=1982, month=11, day=26),
                date(year=2000, month=11, day=26),
                18,
            ],

            # test leap year
            [
                date(year=1996, month=2, day=29),
                date(year=2000, month=2, day=26),
                3,
            ],
            [
                date(year=1996, month=2, day=29),
                date(year=2000, month=2, day=29),
                4,
            ],
            [
                date(year=1996, month=2, day=29),
                date(year=2001, month=3, day=1),
                5,
            ],
        ]

        for entry in data:
            self.assertEqual(calculate_age(entry[0], entry[1]), entry[2])


if __name__ == "__main__":
    unittest.main()