DOC: testing how-to use fixtures / parametrize

[jreback]

I think might be nice to update: http://pandas-docs.github.io/pandas-docs-travis/contributing.html#writing-tests

with how to make / use fixtures and how to use parametrize. something like (and mention that we cannot do this in a class TestClass(...) structure)

Its nice for a beginner to write this up because it will then be from there perspective :>

(pandas) bash-3.2$ more tester.py
import pytest
import numpy as np
import pandas as pd


@pytest.mark.parametrize('dtype', ['int8', 'int16', 'int32', 'int64'])
def test_dtypes(dtype):
    assert str(np.dtype(dtype)) == dtype

@pytest.fixture
def series():
    return pd.Series([1, 2, 3])

@pytest.fixture(params=['int8', 'int16', 'int32', 'int64'])
def dtype(request):
    return request.param

def test_series(series, dtype):
    series = series.astype(dtype)
    assert series.dtype == dtype

and running it

((pandas) bash-3.2$ pytest  tester.py  -v
============================================================================================== test session starts ===============================================================================================
platform darwin -- Python 3.5.2, pytest-3.0.5, py-1.4.31, pluggy-0.4.0 -- /Users/jreback/miniconda3/envs/pandas/bin/python
cachedir: .cache
rootdir: /Users/jreback/pandas, inifile: setup.cfg
plugins: cov-2.4.0, xdist-1.15.0
collected 8 items 

tester.py::test_dtypes[int8] PASSED
tester.py::test_dtypes[int16] PASSED
tester.py::test_dtypes[int32] PASSED
tester.py::test_dtypes[int64] PASSED
tester.py::test_series[int8] PASSED
tester.py::test_series[int16] PASSED
tester.py::test_series[int32] PASSED
tester.py::test_series[int64] PASSED

and lastly about using tm.assert_series_equal and such.

[jorisvandenbossche]

+1 That would be really useful.
I was also personally not yet familiar with pytest, as have to say it is somewhat complex for new contributors/people not familiar with pytest.

What is the reason that it does not work within a Class?

[jreback]

So we have almost all tests defined like this (was the nose style)

class TestFoo(tm.TestCase):

    def test_abc(....):
        self.assertTrue(...)
        self.assertRaises(...)

so this will (and is working) with pytest. But, you cannot use parametrize with this (because ultimately TestCase inherits from unittest.TestCase.

So we have to make these functional (e.g. independent functions), or inherit from object. But THEN we lose the ability to use self.assertTrue(...). However these are easily replaced by

# self.assertTrue
assert this == that

# self.assertRaises(....)
with pytest.raises(....): 
   

[toobaz]

http://pandas.pydata.org/developers.html#testing needs an update too I guess

[jreback]

actually that entire section should simply be a re-direct / rename to http://pandas.pydata.org/pandas-docs/stable/contributing.html that is really old text.

@toobaz you can do a PR if you'd like to: https://github.com/pandas-dev/pandas-website if you'd like.