def test_generate_range():
offset = to_offset("AS")
start = datetime(2000, 2, 12)
end = datetime(2001, 2, 12)
res = generate_range(start, end, offset)
assert isinstance(res, GeneratorType)
dts = list(res)
assert dts[0] == datetime(2000, 1, 1)
assert dts[1] == datetime(2001, 1, 1)
assert dts[2] == datetime(2002, 1, 1)
def test_month_start():
offset = to_offset("MS")
dt = datetime(2001, 2, 12)
res = offset.apply(dt)
assert isinstance(res, datetime)
assert res.year == 2001
assert res.month == 3
assert res.day == 1
res = offset.rollback(dt)
assert res.year == 2001
assert res.month == 2
assert res.day == 1
res = offset.rollforward(dt)
assert res.year == 2001
assert res.month == 3
assert res.day == 1
def test_invalid_offsets(offset_rule):
with pytest.raises(ValueError):
to_offset(offset_rule)