If the url is meant to produce a file rather than a “normal” http response, then its content-type and/or content-disposition will be different.
the response object is basically a dictionary, so you could so something like
self.assertEquals(
response.get('Content-Disposition'),
"attachment; filename=mypic.jpg"
)
more info:
https://docs.djangoproject.com/en/dev/ref/request-response/#telling-the-browser-to-treat-the-response-as-a-file-attachment
UPD:
If you want to read the actual contents of the attached file, you can use response.content. Example for a zip file:
try:
f = io.BytesIO(response.content)
zipped_file = zipfile.ZipFile(f, 'r')
self.assertIsNone(zipped_file.testzip())
self.assertIn('my_file.txt', zipped_file.namelist())
finally:
zipped_file.close()
f.close()