We need to document the new sortable arg in here.

This needs an "Args" section.

This needs an "Args" section.

We can use a set comprehension here:

ids = {
    review_request.get_last_activity_user_id()
    for review_request in object_list
}

You're using this for every test case, so you can just add a class attribute:

class LastUpdatedByColumnTests(BaseColumnTestCase):
    ...
    fixtures = ['test_site']
    ...
    def test_render(self):

Let's wrap this a little differently. Here and in the other test cases below:

review_requests = [
    self.create_review_request(
        summary='Test %d' % index,
        publish=True,
        submitter=username)
    for (index, username) in enumerate(usernames)
]


In fact, since it looks like you are doing that for all the test methods, perhaps move this into a helper function?

This should be in the imperative mood ("Set" instead of "Sets")

Double backticks aren't necessary around the argument names here.

The first line of the docstring should be only one line, and should be in the imperative mood. If you need more detail for completenes, add additional paragraphs.

This should be in the imperative mood ("Return" instead of "Returns"). This docstring also needs a "Returns" section.

id is a built-in for python. Can we use a different variable name?

Add a blank line between these two

We generally avoid the python ternary syntax because it's awkward and confusing. Please just use an if/else here.

I wonder why is "state" being passed as a parameter in this method but it is not being used?

If Review is used multiple times, wouldn't it be better to move this import statement to the global import at the top of the file so there is no need to repeat this import statement multiple times?