There are many ways you can test your software: unit testing, manual testing, end-to-end testing, and so forth. Take a step back and you'll discover even more form of testing, many of them very different in their goals: A/B testing, say, where you see which of two versions of your website results in more signups or ad clicks.
How do these forms of testing differ, how do they relate to each other? How do you choose which kind of testing to pursue, given limited time and resources? How do you deal with strongly held yet opposite views arguing either that a particular kind of testing is essential or that it's a waste time?
This talk will provide you with a model, a way to organize all forms of testing and understand what exactly they provide, and why. Once you understand the model you will be able to choose the right form of testing for your situation and goals.