Python - create unit tests and ensure accurate documentation with doctest

""" 
The doctest module uses class and 
method documentation to run unit 
tests on your code. 
 
The doctest module reads the coding documentation 
you've created and uses that same documentation 
to conduct unit tests.  This helps ensure 
the documentation is accurate and creates a 
one stop destination for documentation and unit 
tests. 
""" 
 
class ExampleClass(object):
    """ 
    Example class that 
    has one working method. 
 
    >>> ec = ExampleClass()
    >>> ec.example(10)
    19 
 
    >>> ec = ExampleClass()
    >>> ec.example(0)
    -1 
 
    # non int parameters should 
    # return nothing 
    >>> ec = ExampleClass()
    >>> ec.example("apple")
 
    >>> ec = ExampleClass()
    >>> ec.a = 3
    >>> ec.example(10)
    30 
    """ 
 
    def __init__(self):
        self.a = 2
        self.b = -1
    def example(self, n):
        try:
            n = int(n)
        except ValueError:
            return None
        return n * self.a + self.b
 
 
if __name__ == '__main__':
    # more about  doctest features  
    import doctest
    doctest.testmod()
 
 
# this outputs: 
# nothing at all 
# if no errors are found then doctest doesn't complain 
 
# If you were to change some of the expected values in the 
# documention....for instance... the last example: 
#    >>> ec = ExampleClass() 
#    >>> ec.a = 3 
#    >>> ec.example(10) 
#    29 
# and change the expected response to 30 
# 
# 
# the output would be: 
#    ********************************************************************** 
#    File "C:\python\docstringexample.py", line 27, in __main__.ExampleClass 
#    Failed example: 
#        ec.example(10) 
#    Expected: 
#        30 
#    Got: 
#        29 
#    ********************************************************************** 
#    1 items had failures: 
#       1 of   9 in __main__.ExampleClass 
#    ***Test Failed*** 1 failures.