Using parametrize for keyword arguments in pytest

Question

I'm learning pytest and I'm trying to use pytest.mark.parametrize for keyword arguments.

This is the simple example without pytest.mark.parametrize:

G = 10
H = 2

def f(g=G, h=H):
    return 5 * g + h

def test_f1():
    assert f(h=4) == 54
    assert f(g=20) == 102

And this is one of my unsuccessful trails using pytest.mark.parametrize. It doesn't work but it helps to understand what I would like to achieve:

import pytest

G = 10
H = 2

def f(g=G, h=H):
    return 5 * g + h  

@pytest.mark.parametrize("arg, expected", [
    ("h=4", 54),
    ("g=20", 102),
    ])

def test_f2(arg, expected):
    assert f(eval(arg)) == expected

Answer 1

The function f accepts keyword arguments, so you need to assign your test parameters to keywords. Luckily, Python provides a very handy way of passing keyword arguments to a function...the dictionary:

d = {'h': 4}
f(**d)

The ** prefix before d will "unpack" the dictionary, passing each key/value pair as a keyword argument to the function.

For your pytest example, this means you just need to replace the string parameter with a dictionary, and the eval in test_f2 with the keyword unpacker:

@pytest.mark.parametrize("arg,expected", [
    ({'h':4}, 54),
    ({'g':20}, 102),
    ])

def test_f2(arg, expected):
    assert f(**arg) == expected