doctest

27 March 2021 - less than 1 min read
Tags: Python Testing


Doctest is a module from Python language’s standard library that allows to generate tests based on output from the standard Python interpreter shell. This module finds patterns in the docstring that looks like interactive shell commands. Docstring usually is used for the description of a class or a function to better understand of the code and its purposes.

Let’s look at the use case of doctest:

def factorial(n):
    '''
    This function calculates recursively and returns
    the factorial of a positive number.
    >>> factorial(2)
    2
    >>> factorial(4)
    24
    '''
    if n <= 1:
        return 1
    return n * factorial(n-1)

To run the test, I use doctest as the main program via the -m option to the interpreter. Usually no output is produced while the tests are running. To make output more verbose, include the -v option.

$ python -m doctest -v file_name.py

Trying:
    factorial(2)
Expecting:
    2
ok
Trying:
    factorial(4)
Expecting:
    24
ok
1 items had no tests:
    file_name
1 items passed all tests:
   2 tests in file_name.factorial
2 tests in 2 items.
2 passed and 0 failed.
Test passed.


See also: