[pytest-dev] Using pytest for the sympy doctests

[Ronny Pfannschmidt]

Hi Oscar,

the doctest plugin inside of pytest is mostly a barebones integration
of the doctest module of the stdlib, adding the pytest extras by adding
onto the default globals of doctest.

As for the output variant, how does sympy decide which one to use,
does the issue happen when the `-s` flag of pytest is used.

my off hand my suggestion would be to make a external pytest-doctest2
plugin to experiment, once its solid i'd be more than happy to drop the
doctest plugin in the core of pytest (as it really only deals with
legacy ways of testing that are best migrated away from)

-- Ronny


Am Sonntag, den 09.12.2018, 01:42 +0000 schrieb Oscar Benjamin:
> Hi all,
> 
> I'm trying to make it possible to use pytest with SymPy. I'm mostly
> there for the main tests now and the next step is to try and get it
> working for the doctests. Currently SymPy has it's own test runner
> which runs the doctests but it works a little differently from the
> standard doctests.
> 
> Firstly SymPy's doctests are required to import all names use in the
> doctest. Standard doctest allows names from the enclosing module to
> be
> used without imports. It's considered important in SymPy that the
> doctests should error out if the imports are not included.
> 
> So for example if I have
> 
> def f():
>     ''''
>     >>> f()
>     42
>     '''
>     return 42
> 
> then this should give an error in the doctests because the function f
> is undefined. A valid doctest for this would look like
> def f():
>     ''''
>     >>> from module import f
>     >>> f()
>     42
>     '''
>     return 42
> 
> It seems there is a feature in sympy to inject symbols into the
> doctest namespace:
> https://docs.pytest.org/en/latest/doctest.html#the-doctest-namespace-fixture
> but I'm really interested in removing things from the namespace to
> test for errors when something isn't properly imported in the
> doctest.
> 
> The other issue is that SymPy has a few different ways of displaying
> output at the terminal: the repr, the ascii version, and the pretty
> version. The doctests are written for the ascii version but under
> pytest the pretty version is found as output. You can see this
> problem
> if you run e.g.
> 
> $ git clone https://github.com/sympy/sympy.git
> $ cd sympy
> $ pytest --doctest-modules sympy/solvers/ode.py
> 
> An example of the failures is
> 
> /Users/enojb/current/sympy/sympy/sympy/solvers/ode.py:1501:
> DocTestFailure
> ___________________ [doctest] sympy.solvers.ode.constant_renumber
> 2896     Only constants in the given range (inclusive) are
> renumbered;
> 2897     the renumbering always starts from 1:
> 2898
> 2899     >>> constant_renumber(C1 + C3 + C4, 'C', 1, 3)
> 2900     C1 + C2 + C4
> 2901     >>> constant_renumber(C0 + C1 + C3 + C4, 'C', 2, 4)
> 2902     C0 + 2*C1 + C2
> 2903     >>> constant_renumber(C0 + 2*C1 + C2, 'C', 0, 1)
> 2904     C1 + 3*C2
> 2905     >>> pprint(C2 + C1*x + C3*x**2)
> Expected:
>                     2
>     C1*x + C2 + C3*x
> Got:
>                     2
>     C₁⋅x + C₂ + C₃⋅x
> 
> To make this work I need to figure out a way for pytest to meet these
> two requirements:
> 1) Customise namespace used for tests
> 2) Customise the function that generates output before comparing with
> expected output of a doctest.
> 
> Does anyone know if it's possible to do either of these things with
> pytest?
> 
> --
> Oscar
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