def test_normal_leap_year():
    assert is_leap(1996)
def test_normal_common_year():
    assert not is_leap(2001)
def test_atypical_common_year():
    assert not is_leap(1900)
def test_atypical_leap_year():
    assert is_leap(2000)
def is_leap(year):
    if year%100==0 and not year%400==0:
        return False
    return year%4==0