Deriving a class from TestCase throws two errors

Question

I have some basic setup/teardown code that I want to reuse in a whole bunch of unit tests. So I got the bright idea of creating some derived classes to avoid repeating code in every test class.

In so doing, I received two strange errors. One, I cannot solve. Here is the unsolvable one:

AttributeError: 'TestDesktopRootController' object has no attribute '_testMethodName' 

Here is my base class:

import unittest import twill import cherrypy from cherrypy._cpwsgi import CPWSGIApp   class BaseControllerTest(unittest.TestCase):      def __init__(self):         self.controller = None      def setUp(self):         app = cherrypy.Application(self.controller)          wsgi = CPWSGIApp(app)          twill.add_wsgi_intercept('localhost', 8080, lambda : wsgi)      def tearDown(self):         twill.remove_wsgi_intercept('localhost', 8080) 

And here is my derived class:

import twill from base_controller_test import BaseControllerTest  class TestMyController(BaseControllerTest):      def __init__(self, args):         self.controller = MyController()         BaseControllerTest.__init__(self)      def test_root(self):         script = "find 'Contacts'"         twill.execute_string(script, initial_url='http://localhost:8080/') 

The other strange error is:

TypeError: __init__() takes exactly 1 argument (2 given) 

The "solution" to that was to add the word "args" to my __init__ function in the derived class. Is there any way to avoid that?

Remember, I have two errors in this one.

Answer 1

It's because you're overriding __init__() incorrectly. Almost certainly, you don't want to override __init__() at all; you should do everything in setUp(). I've been using unittest for >10 years and I don't think I've ever overridden __init__().

However, if you really do need to override __init__(), remember that you don't control where your constructor is called -- the framework calls it for you. So you have to provide a signature that it can call. From the source code (unittest/case.py), that signature is:

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

The safe way to do this is to accept any arguments and just pass 'em up to the base class. Here is a working implementation:

class BaseTest(unittest.TestCase):     def __init__(self, *args, **kwargs):         unittest.TestCase.__init__(self, *args, **kwargs)      def setUp(self):         print "Base.setUp()"      def tearDown(self):         print "Base.tearDown()"   class TestSomething(BaseTest):     def __init__(self, *args, **kwargs):         BaseTest.__init__(self, *args, **kwargs)         self.controller = object()      def test_silly(self):         self.assertTrue(1+1 == 2) 

Answer 2

In BaseController's __init__ you need to call unittest.TestCase's __init__ just like you did in TestMyController.

The call to construct a TestCase from the framework may be passing an argument. The best way to handle this for deriving classes is:

class my_subclass(parentclass):     def __init__(self, *args, **kw):         parentclass.__init__(self, *args, **kw)         ...