testing.py

"""Utilities for testing."""

from typing import Any, Dict

import pytest


def subtests(subtest_dictionary: Dict[str, Dict[str, Any]]):
    """Wrapped pytest.mark.parametrize decorator (to make it more readable).

    For example, instead of:

    @pytest.mark.parametrize(
      'test_input,expected',
      [('3+5', 8), ('6*9', 42)],
      ids=['addition', 'multiplication'])
    def test_eval(test_input, expected):
      assert eval(test_input) == expected

    this allows to write:

    @subtests({
      'addition': dict(
        test_input='3+5',
        expected=8
      ),
      'multiplication': dict(
        test_input='6*9',
        expected=42
      )
    })
    def test_eval(test_input, expected):
      assert eval(test_input) == expected

    which is more readable, especially when defining many subtests.

    Args:
      subtest_dictionary: Dictionary of dictionaries, where the keys of the outer
        dictionary are the subtest ids, and the inner dictionary contains subtest
        parameters stored as key: value pairs of the form argname: argvalue. Since
        pytest.mark.parametrize works with positional arguments only, all subtests
        must specify the same set of arguments, or the function will throw a
        KeyError.

    Returns:
      The equivalent pytest.mark.parametrize fixture (see example above).
    """
    argnames = set()
    for v in subtest_dictionary.values():
        for k in v.keys():
            argnames.add(k)
    argnames = sorted(argnames)
    return pytest.mark.parametrize(
        argnames=argnames,
        argvalues=[[v[k] for k in argnames] for v in subtest_dictionary.values()],
        ids=subtest_dictionary.keys(),
    )