Avoid converting functions to methods in a class

[Steven D'Aprano]

I have a convention when writing unit tests to put the target of the test 
into a class attribute, as follows:

class MyTest(unittest.TestCase):
    target = mymodule.someclass

    def test_spam(self):
        """Test that someclass has a spam attribute."""
        self.failUnless(hasattr(self.target, 'spam'))


It works well until I write a test for stand-alone functions:

class AnotherTest(unittest.TestCase):
    target = mymodule.function

    def test_foo(self):
        self.assertEquals(self.target('a', 'b'), 'foo')

The problem is that target is turned into a method of my test class, not 
a standalone function, and I get errors like:

TypeError: function() takes exactly 2 arguments (3 given)

The solution I currently use is to drop the target attribute in this 
class, and just refer to mymodule.function in each individual test. I 
don't like this solution because it violates Once And Only Once: if the 
function changes name, I have to make many edits to the test suite rather 
than just one.

Are there any better solutions?


-- 
Steven