Agile drives frequent releases and frequent releases drive automated testing. You can't just switch on test automation though, there is a lot of investment in time and energy required and the payoff is usually in the medium to long term.
I have a long-running debate with a friend of mine about the state of software development.
I argue that by applying agile best practice the majority of software projects can be successful. My friend counters this argument by saying the trouble is that nobody ever applies agile best practice, so software projects continue to fail.
In many ways my friend is right, in the real world agile is often badly applied. The reason why this is has puzzled me for many years.
Even if I don't know how to implement something I can almost always write a test for it and If I can't figure out how to write a test for it I have no business programming it in the first place. - Kent Beck
Many processes in agile are mutually supporting. A good example of this is testing and its relationship to the development iteration.
