Code review comment for lp:~james-w/linaro-image-tools/fetch-packages

As for the code, I think it's by and large fine, bearing in mind that I don't know how python-apt works.

I don't know if the stuff in testing.py needs tests, but it certainly needs documentation. I also wonder if AptSource should be called AptSourceFixture or something.

DummyProgress could use a docstring. After all that effort going to silencing python-apt, some kind of progress is likely to be desired, I think... I guess this can be carefully added back in later.

fetch_packages doesn't document its return type correctly any more.

All else looks good.