import unittest
from selenium import selenium


class SetupSomething(unittest.TestCase):

    def setUp(self, URL):

        self.selenium = selenium("localhost", 4444, "*firefox", self.URL)
        

    def tearDown(self):
        pass


class TestSomething(SetupSomething):
    def __init__():
        print "bug."
    
    def setUp(self):
        self.URL = "http://google.com/"

    def tearDown(self):
        pass

    def test_tester(self):
        self.selenium.open('/')
        print "no"
        


unittest.main()

----
TypeError: '__init__() takes no arguments (2 given)'

Definitely it does not look like a bug.

>>> import unittest
>>> help(unittest.TestCase)

...

 |  If it is necessary to override the __init__ method, the base class
 |  __init__ method must always be called. It is important that subclasses
 |  should not change the signature of their __init__ method, since instances
 |  of the classes are instantiated automatically by parts of the framework
 |  in order to be run.

...

What flox said.

There's no reversal here:  you've defined an __init__ method that takes no arguments.  The unittest framework tries to instantiate a TestSomething instance by calling it with two arguments (one of which is self).  If you look at the source for the TestCase class you'll see:

    def __init__(self, methodName='runTest'):
        ...


Note that the message you're seeing applies to *your* __init__ method:  that method expects no arguments (because that's the way you defined it), but it's getting two (because the unittest test runner calls it that way).