[Python-Dev] r87389 - in python/branches/py3k: Doc/library/unittest.rst Lib/unittest/case.py Misc/NEWS

[Nick Coghlan]

On Tue, Dec 21, 2010 at 1:31 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
>> Diffing is completely an implementation detail of how the failure
>> messages are generated. The important thing is that failure messages
>> make sense with respect to actual result and expected result.
>
> Which, again, they don't. Let's see:
>
>    self.assertEqual(actual, expected)
> AssertionError: 'a\nb\nc\ne\n' != 'a\nb\nc\nd\n'
>  a
>  b
>  c
> - e
> + d
>
> The diff shows "expected - actual", but it would be logical (in your own
> logic) to display "actual - expected". The whole issue disappears if you
> drop this idea of naming the arguments "actual" and "expected".

To make this a bit clearer...

>>> class Ex(ut.TestCase):
...   def demo(self):
...     self.assertEqual("actual", "expected")
...
>>> Ex("demo").demo()
Traceback (most recent call last):
  <snip TB details>
AssertionError: 'actual' != 'expected'
- actual
+ expected

For the actual/expected terminology the diff is the wrong way around
(as of 3.2b1, anyway).

My own +1 goes to keeping the actual/expected terminology (and
ordering) and adjusting the diffs accordingly (with a header noting
that the diff is old=expected, new=actual).

assertRaises() *is* an exception to the general actual/expected
pattern, but that asymmetry is forced by the ability to pass arbitrary
positional arguments to the function being tested (which later proved
useful for the context manager form as well).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia