freezegun does not work with datetime.astimezone()

[lalten]

freezegun does not work with datetime.astimezone()

❯ ipython
Python 3.8.10 (default, Jun 22 2022, 20:18:18)
Type 'copyright', 'credits' or 'license' for more information
IPython 8.5.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import datetime

In [2]: now = datetime.datetime.now(tz=datetime.timezone.utc)

In [3]: now.isoformat()
Out[3]: '2022-10-19T10:25:03.584218+00:00'

In [4]: now.astimezone().isoformat()
Out[4]: '2022-10-19T12:25:03.584218+02:00'

But

	import datetime
	
    @freeze_time("2000-01-01T00:00:00.000Z", tz_offset=3)
    def test_timezone() -> None:
        now = datetime.datetime.now(tz=datetime.timezone.utc)
        assert now.isoformat() == "2000-01-01T03:00:00+00:00"
>       assert now.astimezone().isoformat() == "2000-01-01T06:00:00+03:00"
E       AssertionError: assert '2000-01-01T03:00:00+00:00' == '2000-01-01T06:00:00+03:00'
E         - 2000-01-01T06:00:00+03:00
E         ?             ^        ^
E         + 2000-01-01T03:00:00+00:00
E         ?             ^        ^

Relevant datetime source is here:
https://github.com/python/cpython/blob/main/Lib/datetime.py#L1963-L1998

Problematic line in freezegun is here:

freezegun/freezegun/api.py

Line 368 in 9d5ea73

tz = tzlocal()

Workaround:

import datetime
import dateutil.tz
from unittest import mock

@mock.patch("freezegun.api.tzlocal", lambda: dateutil.tz.tzoffset("", datetime.timedelta(hours=3)))
@freeze_time("2000-01-01T00:00:00.000Z", tz_offset=3)
def test_timezone() -> None:
    now = datetime.datetime.now(tz=datetime.timezone.utc)
    assert now.isoformat() == "2000-01-01T03:00:00+00:00"
    assert now.astimezone().isoformat() == "2000-01-01T06:00:00+03:00"