Detect CI via environment variable

CI systems typically set the environment variable CI as a de facto standard for easy CI detection. Here are details of several popular CI services:

Pytest handles conditional tests well. This allows skipping a subset of tests on CI by detecting the CI environment variable:

import os
import pytest

CI = os.environ.get('CI') in ('True', 'true')

@pytest.mark.skipif(CI, reason="not a test for CI")
def test_myfun():