pytest plugin: avoid repeating arguments in parametrize

This is an alternative to the rejected pull request #780 of pytest.

Installation

Just get it from PyPI:

python3 -m pip install pytest-auto-parametrize --user

Usage

This is an example for the usage of a parametrized test without using this plugin:

import pytest

testparams = [
    (1, 2, 3, 4, 5, 6, 7),
    (7, 6, 5, 4, 3, 2, 1),
]

@pytest.mark.parametrize('a, b, c, d, e, f, g', testparams)
def test_many_args(a, b, c, d, e, f, g):
    assert d == 4

The argument list has to be repeated, which is annoying.

By using this plugin, the repetition can be avoided:

import pytest

testparams = [
    (1, 2, 3, 4, 5, 6, 7),
    (7, 6, 5, 4, 3, 2, 1),
]

@pytest.auto_parametrize(testparams)
def test_many_args(a, b, c, d, e, f, g):
    assert d == 4

The auto-deduced parameters must be in the beginning of the parameter list, but any other parameters can be used afterwards, e.g. fixtures:

import pytest

testparams = [
    (1, 2, 3, 4, 5, 6, 7),
    (7, 6, 5, 4, 3, 2, 1),
]

@pytest.fixture
def myfixture():
    return 4

@pytest.auto_parametrize(testparams)
def test_many_args_and_fixture(a, b, c, d, e, f, g, myfixture):
    assert d - myfixture == 0

Limitations

Unlike @pytest.mark.parametrize(...) the decorator @pytest.auto_parametrize(...) cannot be used multiple times for the same test function. It can be used together with one or multiple instances of @pytest.mark.parametrize(...), though, as long as the "auto" arguments are in the beginning of the argument list.