How to show the error messages caught by assertRaises() in unittest in Python2.7?

Out-of-the-box unittest doesn't do this. If this is something you want to do frequently, you can try something like this:

class ExtendedTestCase(unittest.TestCase):

  def assertRaisesWithMessage(self, msg, func, *args, **kwargs):
    try:
      func(*args, **kwargs)
      self.assertFail()
    except Exception as inst:
      self.assertEqual(inst.message, msg)

Derive your unit test classes from ExtendedTestCase instead of unittest.TestCase.

But really, if you're simply concerned about misspelled error messages, and concerned enough to want to build test cases around it, you shouldn't be inlining messages as string literals. You should do with them what you do with any other important strings: defining them as constants in a module that you import and that someone is responsible for proofreading. A developer who misspells words in his code will also misspell them in his test cases.

You are looking for assertRaisesRegex, which is available since Python 3.2. From the docs:

self.assertRaisesRegex(ValueError, "invalid literal for.*XYZ'$",
                       int, 'XYZ')

or:

with self.assertRaisesRegex(ValueError, 'literal'):
    int('XYZ')

PS: if you are using Python 2.7, then the correct method name is assertRaisesRegexp.

I once preferred the most excellent answer given above by @Robert Rossney. Nowadays, I prefer to use assertRaises as a context manager (a new capability in unittest2) like so:

with self.assertRaises(TypeError) as cm:
    failure.fail()
self.assertEqual(
    'The registeraddress must be an integer. Given: 1.0',
    str(cm.exception)
)