The Foobar coding challenge seems to work really for Google, for whatever reason.

Go to Google and search "python list comprehension" in a bunch of different tabs. Make sure it's exactly that. If you have an extra 's', or if you do "list comprehension python", it's not gonna work.

If you go through the first 3 levels, then they'll ask you to send in a resume.

Admittedly, I only know results from the perspective of students, but I know several people who were initially rejected that got callbacks after finishing Foobar.