unit test for a printing method

[Scott David Daniels]

noro wrote:
> What is the proper way to test (using unit test) a method that print
> information?
> for example:
> 
> def A(s):
>          print '---'+s+'---'
> 
> and i want to check that A("bla") really print out "---bla---"
> 
> thanks
> amit
> 

For silly module myprog.py:
     def A(s):
         print '---'+s+'---'


in test_myprog.py:
     import unittest
     from cStringIO import StringIO  # or  from StringIO ...
     import sys
     import myprog

     class SomeIOTests(unittest.TestCase):
         def setUp(self):
             self.held, sys.stdout = sys.stdout, StringIO()

         def test_trivialArg(self):
             myprog.A('')
             self.assertEqual(sys.stdout.getvalue(), '------\n')

         def test_simpleArg(self):
             myprog.A('simple')
             self.assertEqual(sys.stdout.getvalue(), '---simple---\n')

         def tearDown(self):
             sys.stdout = self.held

     if __name__ == '__main__':
         unittest.main()

--Scott David Daniels
scott.daniels at acm.org