What you hear about is mostly Scrum. And Scrum doesn't deal with technical practices. And many consider that failing of Scrum, as adoption of Scrum without adoption of proper technical practices results in "Flaccid-Scrum".
eXtreme Programming, which is much less known and adopted Agile practice, on the other hand does deal with technical practices great deal. Technical practices like automated testing, refactoring, pair programming and continuous deployment are at heart of XP. And XP believes it is those practices that allow fast, sustainable and predictable development.