Software testing is important, we all know that. It's laborious, error-prone, boring and expensive, we know that too. That makes testing the right candidate for automation.
There are several dimensions of the problem of software testing:
The area provides us with a rich treasure of interesting problems. Research in software testing, therefore, aims to reduce the labour-intensiveness of this unavoidable but uninteresting software engineering activity. In there, you get to use everything interesting you have learnt in computer science.