pytest parameterized test with custom id function

Question

I have a parameterized test which takes str, and dict as an argument and so the name look pretty weird if I allow pytest to generate ids.

I want to generate custom ids using a function, however it seems it's not working as intended.

def id_func(param):
    if isinstance(param, str):
        return param


@pytest.mark.parametrize(argnames=('date', 'category_value'),
                         argvalues=[("2017.01", {"bills": "0,10", "shopping": "100,90", "Summe": "101,00"}),
                                    ("2017.02", {"bills": "20,00", "shopping": "10,00", "Summe": "30,00"})],
                         ids=id_func)
def test_demo(date, category_value):
    pass

I was thinking it would return something like this

test_file.py::test_demo[2017.01] PASSED
test_file.py::test_demo[2017.02] PASSED

but it's returning this.

test_file.py::test_demo[2017.01-category_value0] PASSED
test_file.py::test_demo[2017.02-category_value1] PASSED

Could someone tell me what's wrong with this, or is there any way to achieve this?

Update:

I realize what's the issue, if_func will be called for each parameter and if I won't return str for any parameter default function will be called. I have fix but that's also ugly.

def id_func(param):
    if isinstance(param, str):
        return param
    return " "

Now it returns something like this,

test_file.py::test_demo[2017.01- ] PASSED
test_file.py::test_demo[2017.02- ] PASSED

The problem is even If I return empty string (i.e. return "" )it takes the default representation. Could someone let me know why?

Answer 1

One way is to move your argvalues to another variable and write your test like this:

import pytest


my_args = [
      ("2017.01", {"bills": "0,10", "shopping": "100,90", "Summe": "101,00"}),
      ("2017.02", {"bills": "20,00", "shopping": "10,00", "Summe": "30,00"})
]


@pytest.mark.parametrize(
    argnames=('date', 'category_value'), argvalues=my_args,
    ids=[i[0] for i in my_args]
)
def test_demo(date, category_value):
    pass

Test execution:

$ pytest -v tests.py 
================= test session starts =================
platform linux2 -- Python 2.7.12, pytest-3.2.1, py-1.4.34, pluggy-0.4.0 -- /home/kris/.virtualenvs/2/bin/python2
cachedir: .cache
rootdir: /home/kris/projects/tmp, inifile:
collected 2 items                                      

tests.py::test_demo[2017.01] PASSED
tests.py::test_demo[2017.02] PASSED

============== 2 passed in 0.00 seconds ===============

I think it's not possible with a function (idfn in your case), because if it's not generating label for an object the default pytest representation is used.
Check pytest site for details.