Python doctests for inline testing

Python’s doctest module allows you to write tests directly in docstrings by mimicking interactive Python sessions. Simply write >>> followed by Python code and the expected output on the next line.

def add(a, b):
    """
    Add two numbers.
    
    >>> add(2, 3)
    5
    >>> add(-1, 1)
    0
    """
    return a + b

Run with python -m doctest filename.py or include doctest.testmod() in your script. Great for keeping examples and tests close to the code they document.