Configures and runs Python's stdlib doctest - embeds executable test cases in docstrings using `>>>` Python interactive prompt convention; supports `# doctest: +ELLIPSIS` / `+NORMALIZE_WHITESPACE` / `+SKIP` directives; integrates with pytest via `--doctest-modules` flag; runs as `python -m doctest module.py -v`. Use for self-documenting reference implementations + simple smoke-test coverage embedded in API docs.