The Django framework version 1.4 added much better integration with Selenium for in-browser functional testing. This made Test-Driven Development an even more obvious decision for our new Liquid Galaxy Content Management System. This went very well until we needed to test file uploads in the Django admin interface.
To work around this limitation, Ryan Kelly developed a Middleware to emulate successful file uploads for automated testing. This middleware inserts additional hidden fields into any forms sent to the client. Setting their value causes a file upload to happen locally on the server. (I used a slightly newer version of this Middleware from another project.)
This is a lot of hoops to jump through, but now we have functional tests for file uploads and their post-upload processing. Hopefully the Selenium or Django projects can develop a better-supported method for file upload testing.