Using doctest

https://docs.python.org/3/library/doctest.html

https://www.python-course.eu/python3_tests.php

INTRODUCTION

The 'doctest' module searches for pieces of text that look like interactive Python sessions, and then executes those sessions to verify that they work exactly as shown.

# Simple usage: checking examples in docstrings.

# Content of the file fib4.py

def fibonacci(n):
    """
    Calculates the n-th Fibonacci number iteratively.

    >>> fibonacci(0)
    0
    >>> fibonacci(1)
    1
    >>> fibonacci(10)
    55
    >>> fibonacci(15)
    610
    >>>

    """
    old, new = 0, 1
    for _ in range(n):
        old, new = new, old + new
    return old

if __name__ == "__main__":
    import doctest
    doctest.testmod()

# To execute tests:

$ python fib4.py
$               # no output = no errors
$ python fib4.py -v   # verbose mode
Trying:
    fibonacci(0)
Expecting:
    0
ok
Trying:
    fibonacci(1)
Expecting:
    1
ok
Trying:
    fibonacci(10)
Expecting:
    55
ok
Trying:
    fibonacci(15)
Expecting:
    610
ok
1 items had no tests:
    __main__
1 items passed all tests:
   4 tests in __main__.fibonacci
4 tests in 2 items.
4 passed and 0 failed.
Test passed.

$ python -m doctest fib5.py -v   # without the 'if' part

# Simple usage: checking examples in a text file.

import doctest
doctest.testfile("example.txt")
# The file content is treated as if it were a single giant docstring.