Option to show full assertion diff

[pytestbot]

Originally reported by: Wolfgang Schnerring (BitBucket: wosc, GitHub: wosc)

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If you compare e.g. a larger dict and the assertion fails, the output is truncated with ellipses in it -- which sometimes hide exactly the parts that differ ("{'foo': 'bar', ... } != {'foo': 'bar', ...}"). Even passing -v doesn't help.

I've looked at _pytest.util._compare_eq_dict, it uses py.io.saferepr, which in turn has a maxlength parameter, but pytest does not use that -- I guess it should.

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• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/381

[pytestbot]

Original comment by Floris Bruynooghe (BitBucket: flub, GitHub: flub):

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Hi, I believe this is already fixed. Currently you get this:

cd; py.test /tmp/sandbox/test_foo.py
============================================= test session starts ==============================================
platform linux2 -- Python 2.7.4 -- pytest-2.4.3.dev2
collected 1 items 

../../tmp/sandbox/test_foo.py F

=================================================== FAILURES ===================================================
__________________________________________________ test_dict ___________________________________________________

    def test_dict():
        a = {'aaaaaa': 'bbbbbb',
             'cccccc': 'dddddd',
             'eeeeee': 'ffffff',
             'gggggg': 'hhhhhh',
             'iiiiii': 'jjjjjj'}
        b = {'aaaaaa': 'bbbbbb',
             'cccccc': 'dddddd',
             'eeeeee': 'ffffff',
             'gggggg': 'hhhhhh',
             'iiiiii': 'kkkkkk'}
>       assert a == b
E       assert {'aaaaaa': 'b...'hhhhhh', ...} == {'aaaaaa': 'bb...'hhhhhh', ...}
E         Omitting 4 identical items, use -v to show
E         Differing items:
E         {'iiiiii': 'jjjjjj'} != {'iiiiii': 'kkkkkk'}

/tmp/sandbox/test_foo.py:12: AssertionError
=========================================== 1 failed in 0.01 seconds ===========================================

And with -v:

cd; py.test /tmp/sandbox/test_foo.py -v
============================================= test session starts ==============================================
platform linux2 -- Python 2.7.4 -- pytest-2.4.3.dev2 -- /home/flub/.virtualenvs/pytest/bin/python
collected 1 items 

../../tmp/sandbox/test_foo.py:1: test_dict FAILED

=================================================== FAILURES ===================================================
__________________________________________________ test_dict ___________________________________________________

    def test_dict():
        a = {'aaaaaa': 'bbbbbb',
             'cccccc': 'dddddd',
             'eeeeee': 'ffffff',
             'gggggg': 'hhhhhh',
             'iiiiii': 'jjjjjj'}
        b = {'aaaaaa': 'bbbbbb',
             'cccccc': 'dddddd',
             'eeeeee': 'ffffff',
             'gggggg': 'hhhhhh',
             'iiiiii': 'kkkkkk'}
>       assert a == b
E       assert {'aaaaaa': 'b...'hhhhhh', ...} == {'aaaaaa': 'bb...'hhhhhh', ...}
E         Common items:
E         {'aaaaaa': 'bbbbbb',
E          'cccccc': 'dddddd',
E          'eeeeee': 'ffffff',
E          'gggggg': 'hhhhhh'}
E         Differing items:
E         {'iiiiii': 'jjjjjj'} != {'iiiiii': 'kkkkkk'}

/tmp/sandbox/test_foo.py:12: AssertionError
=========================================== 1 failed in 0.01 seconds ==========================================

Certainly this second option shows you all items in the dictionary, although I'll admit not as a straight diff.

Feel free to re-open if you disagree or I misunderstood this.