conftest.py

# The code here has been borrowed from the examples given here:
# https://docs.pytest.org/en/latest/example/simple.html
import pytest


def pytest_addoption(parser):
    parser.addoption(
        "--run-slow",
        action="store_true",
        default=False,
        help="run tests marked as slow",
    )


def pytest_configure(config):
    slow_info = "slow: mark test as slow to run"
    neg_info = "negative: marks tests that test invalid input"
    config.addinivalue_line("markers", slow_info)
    config.addinivalue_line("markers", neg_info)


def pytest_collection_modifyitems(config, items):
    if config.getoption("--run-slow"):
        return
    skipped = pytest.mark.skip(
        reason="slow tests are skipped by default; to run, call pytest with --run-slow."
    )
    for item in items:
        if "slow" in item.keywords:
            item.add_marker(skipped)