Friday, August 12, 2011

From the frontline, day 5

Another day, another piece of testing mayhem. I've completed the 0.1 version of my Flask-Downloader helper class. With this, I could complete my web app. Now, the downloader itself has a bunch of tests to make sure it's working as expected, but I was also going to test the corresponding code paths in the web app's tests.
The user can provide the input either by uploading a file or by giving an accession number. Testing for the file uploads was easy, as the Flask test client accepts file-like objects as data input for POST requests. So testing the app will do the right thing is as easy as:
def test_upload(self):
    file_handle = open(tmp_filename)
    data = dict(file=file_handle)
    rv ='/upload', data=data)
    assert "upload succeeded" in
Assuming your upload function listens on '/upload' and returns a page that contains "upload ducceeded", of course.
Testing file downloads is a bit more elaborated, because I don't actually want my downloader to connect to the internet during a test run. Minimock to the rescue! I can fake the download helper and create the same kind of output to fool the application code.
from minimock import Mock
from werkzeug import FileStore
def test_download(self):
    data = dict(id="FAKE")
    # now create the fake downloader
    tmp_file = open(tmp_file_path) = Mock('') = FileStore(stream=tmp_file)
     rv ='/download', data=data)
    assert "download succeeded" in
With similar assumptions as in the example before, and also the idea that you have a pre-existing file in tmp_file_path. A StringIO file-like object should do the trick as well.
With all the tests in place and a test coverage of 100%, I declare this campaign a success. I still need to deploy the new web app on my test server instead of the old one, but I'm going to do that next week. I will also continue my war on legacy code, now tackling the pieces that do the actual work. No war is over as quick as you'd initially hope after all. Also, I'm pretty sure the 100% code coverage don't mean there's not plenty of places for bugs to hide in, just that at least all of the code is looked at by the interpreter once. Still, it's a good conclusion to a busy week. Testing rocks.


Pronoy said...


I was wondering why didn't you go for this directly?

Kai said...

Because I don't really need to serve out uploaded files again but am doing computation on those and serve out the result. Flask-Uploads really just adds flexibility where I don't need any.