make sure fromtimestamp always return FakeDateTime

[Koswu]

This fix #344

This is my first PR, if something goes wrong, please let me know, PTAL

[boxed]

The proposed code change seems to be no change of behavior. Could you point out what it changes?

[Koswu]

In the fromtimestamp method, when the tz parameter is None, It will return the real datetime object. This object's .timestamp() behavior will depend on the system timezone, even it tzinfo is None. For example:

# my system timezone is UTC+8
>>> dt = datetime.datetime(1970, 1, 1, 8, 0, 1)
>>> dt.tzinfo
None
>>> dt.timestamp()
1.0

However, the fake one depend on the freeze time zone:

>>> freezer = freeze_time(datetime.datetime(1970, 1, 1, 0, 0, 1), tz_offset=-1)
>>> freezer.start()
>>> datetime.datetime(1970, 1, 1, 8, 0, 1).timestamp()
32401.0

So if we make these steps:

1. make a fake datetime object
2. convert it to timestamp
3. convert it to datetime
4. convert it to timestamp

we will have a type chain like this:

FakeDatetime -> int -> RealDatetime -> int

Since we know there are different behavior between FakeDatetime.timestamp() and RealDatetime.timestamp(), it will cause problem that two timestamp in the type chain are not equal.

That's why I added the test.

[bblommers]

Suggested change

	result = datetime_to_fakedatetime(real_datetime.fromtimestamp(t, tz))
	result = real_datetime.fromtimestamp(t, tz)

The datetime_to_fakedatetime already happens at the end - no need to duplicate this call.

Happy to merge once that's fixed.

[Koswu]

fixed. thanks for pointing this out.

[bblommers]

Great - thanks for the fix @Koswu!