How to write tests in Python using doctest

Python’s built-in doctest module provides a lightweight way to combine documentation and executable tests within function, class, or module docstrings, reducing the need for separate test scripts. The tutorial explains that docstrings differ from ordinary comments by documenting how code should be used, while doctest recognizes examples formatted like interactive Python sessions, with `>>>` marking commands and subsequent lines representing expected output. Using a simple `square` function, it demonstrates embedding input-output examples in the function’s initial docstring, importing doctest, and running `doctest.testmod()` when the module is executed. Tests can be run from the terminal normally, with verbose output using `-v`, or directly through Python’s doctest command-line interface. The article also shows how docstrings can specify parameter and return types, and concludes that doctests can improve readability, preserve requirements and edge cases near the code, and make basic Python testing more efficient.

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