Doctest¶

The Python module doctest checks whether tests in a docstring or in another text file are fulfilled.

In arithmetic.py you can add the following docstring:

def divide(x, y):
    """Divides the first parameter by the second
    >>> x, y, z = 7, -6.0, 0
    >>> divide(x, y)
    -1.1666666666666667
    >>> divide(x, z)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ZeroDivisionError: division by zero
    """

Then you can test it with:

Linux/macOS

$ python -m doctest test/arithmetic.py -v
Trying:
    add(7,6)
Expecting:
    13
ok
Trying:
    x, y, z = 7, -6.0, 0
Expecting nothing
ok
Trying:
    divide(x, y)
Expecting:
    -1.1666666666666667
ok
Trying:
    divide(x, z)
Expecting:
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ZeroDivisionError: division by zero
ok
Trying:
    multiply(7,6)
Expecting:
    42
ok
Trying:
    subtract(7,6)
Expecting:
    1
ok
1 items had no tests:
    arithmetic
4 items passed all tests:
   1 tests in arithmetic.add
   3 tests in arithmetic.divide
   1 tests in arithmetic.multiply
   1 tests in arithmetic.subtract
6 tests in 5 items.
6 passed and 0 failed.
Test passed.

Windows

C:> python -m doctest arithmetic.py -v
Trying:
    add(7,6)
Expecting:
    13
ok
Trying:
    x, y, z = 7, -6.0, 0
Expecting nothing
ok
Trying:
    divide(x, y)
Expecting:
    -1.1666666666666667
ok
Trying:
    divide(x, z)
Expecting:
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ZeroDivisionError: division by zero
ok
Trying:
    multiply(7,6)
Expecting:
    42
ok
Trying:
    subtract(7,6)
Expecting:
    1
ok
1 items had no tests:
    arithmetic
4 items passed all tests:
   1 tests in arithmetic.add
   3 tests in arithmetic.divide
   1 tests in arithmetic.multiply
   1 tests in arithmetic.subtract
6 tests in 5 items.
6 passed and 0 failed.
Test passed.

So that the doctests can also be imported into other modules, you should add the following lines:

if __name__ == "__main__":
    import doctest

    doctest.testmod(verbose=True)