anybox.testing.datetime 0.4

Various utilities related to date and time for testing purposes.

A module to allow cheating with current time in tests.
======================================================

This README is also a doctest. To it and other doctests for this package,
simply do::

nosetests --with-doctest --doctest-extension=txt

Usage
~~~~~

Before anything, the package must be imported in order to replace the
regular ``datetime`` module with the modified one::

>>> import anybox.testing.datetime
>>> from datetime import datetime
>>> import time

Let's keep the real value of ``now`` around::

>>> start = datetime.now()
>>> start_t = time.time()

Then you can::

>>> datetime.set_now(datetime(2001, 01, 01, 3, 57, 0))
>>> datetime.now()
datetime(2001, 1, 1, 3, 57)
>>> datetime.today()
datetime(2001, 1, 1, 3, 57)

The time module goes along::

>>> datetime.fromtimestamp(time.time())
datetime(2001, 1, 1, 3, 57)

Note that you can expect a few microseconds difference (not displayed
here because ``datetime.fromtimestamp`` ignores them).


Don't forget afterwards get back to the regular system clock, otherwise
many pieces of code might get very suprised if the system clock looks as if
it's frozen::

>>> datetime.real_now()

Now let's check it worked::

>>> now = datetime.now()
>>> now > start
True
>>> from datetime import timedelta
>>> now - start < timedelta(0, 0, 10000) # 10 ms
True

And with the ``time`` module::

>>> now_t = time.time()
>>> now_t > start_t
True
>>> now_t - start_t < 0.01 # 10 ms again
True

Other constructors are still available (this is a non regression
test)::

>>> import datetime
>>> datetime.time(3, 57, 0)
datetime.time(3, 57)
>>> datetime.datetime(2013, 1, 1, 3, 57, 0)
datetime(2013, 1, 1, 3, 57)
>>> datetime.date(2013, 1, 1)
datetime.date(2013, 1, 1)

Behind the hood
~~~~~~~~~~~~~~~

Our replacement class is the one loaded from the ``datetime`` module,
but instances of the original ``datetime`` class behave exactly as
instances of our ``datetime.datetime``. This is needed because most
computational methods, actually return an object of the original
``datetime`` class. This works with python >= 2.6 only.

First let's check that our class is a subclass of the original
one. If this fails, this test does not mean anything anymore::

>>> datetime.datetime is datetime.original_datetime
False
>>> issubclass(datetime.datetime, datetime.original_datetime)
True

Then let's demonstrate the behaviour::

>>> odt = datetime.original_datetime(2012, 1, 1)
>>> isinstance(odt, datetime.datetime)
True
>>> issubclass(datetime.original_datetime, datetime.datetime)
True

We'll need a ``tzinfo`` subclass from now on.

>>> from datetime import tzinfo
>>> class mytzinfo(tzinfo):
... def utcoffset(self, dt):
... return timedelta(hours=2)
... def dst(self, dt):
... return timedelta(0)

Compatibility
~~~~~~~~~~~~~

Over the lifespan of this development toolkit module, we've had to ensure
compatibility with several subsystems

SQLite
------

Also, ``sqlite3`` does recognize our ``datetime`` and ``date`` classes as
if they were the original ones::

>>> import sqlite3
>>> cnx = sqlite3.connect(':memory:')
>>> cr = cnx.cursor()
>>> cr = cr.execute("CREATE TABLE dates (dt text, d text)")
>>> dt = datetime.datetime(2013, 1, 25, 12, 34, 0)
>>> d = datetime.date(2013, 4, 7)
>>> cr = cr.execute("INSERT INTO dates VALUES (?, ?)", (dt, d))
>>> cr = cr.execute("SELECT dt, d from dates")
>>> cr.fetchall()
[(u'2013-01-25 12:34:00', u'2013-04-07')]

Now let's try this again with the original ones::

>>> dt = datetime.datetime.now()
>>> isinstance(dt, datetime.original_datetime)
True
>>> d = datetime.date.today()
>>> cr = cr.execute("INSERT INTO dates VALUES (?, ?)", (dt, d))
>>> cr = cr.execute("SELECT dt, d from dates")
>>> res = cr.fetchall() # can't check the value, it changes a lot !
Version 0.4 (unreleased)
------------------------
- #3: fixed compatibility problem with ``sqlite3`` (spotted via IPython/IPdb)

Version 0.3.1 (2012-11-28)
--------------------------

- #1: tested code using time zone optional arg of now() doesn't break
any more (no real time zone support, though)

Version 0.3 (2012-11-23)
------------------------

- Fixed the problem that ``datetime`` objects generated from
computations used to fail ``isinstance`` tests.

Version 0.2.1 (2012-11-22)
--------------------------

- Fixed issue with ``datetime.time`` masking

Version 0.1 (2012-07-15)
------------------------
- initial version