Code snippet to accompany blogpost on 5 pytest best practices

test_tmpdir.py

import pytest


def process_file(fp):
    """Toy function that returns an array of line lengths."""
    return [len(l.strip()) for l in fp.readlines()]


@pytest.mark.parametrize("filename, expected", [
    ("first.txt", [3, 3, 3]),
    ("second.txt", [5, 5]),
])
def test_antipattern(filename, expected):
    with open("resources/" + filename) as fp:
        assert process_file(fp) == expected


@pytest.mark.parametrize("contents, expected", [
    ("foo\nbar\nbaz", [3, 3, 3]),
    ("hello\nworld", [5, 5]),
])
def test_pattern(tmpdir, contents, expected):
    tmp_file = tmpdir.join("testfile.txt")
    tmp_file.write(contents)
    with tmp_file.open() as fp:
        assert process_file(fp) == expected