There is a pretty good online course about software testing in Udacity, called How to Make Software Fail by John Regehr and Sean Bennett.
This course is for programmers, but testers can also find some useful thing in it, especially the automation testers.
There are some brief quizzes and answers with explanations. They are not necessary of course, so you may just listen the theoretical part, which takes a few hours. In the some exercises you should program a code in python, others are just theoretical questions.
As always in Udacity there are a discussion and a wiki sections - in the wiki you can find the whole written text of the course.
Technical part: Auto-Next function does not perfectly work in Safari browser - sometimes it doesn't switch to the next video automatically. In Chrome works perfectly.
Answers' submitting works only if you're signed in, otherwise it just "working" a long while (Safari, Chrome). But you can watch videos without submitting answers, so it is not really necessary to sign up.
And here is the interesting example of one video: