tl;dr:Research shows that: (1) Self-interruptions i.e. voluntary task switching is more disruptive than external interruptions. (2) Developers self-reported that external interruptions are more disruptive than self-interruptions. (3) Contextual factors such as time of day are a stronger determinant of how disruptive an interruption might be than task-specific factors. (4) Switching between programming and testing tasks, compared to other development tasks, makes developers more vulnerable to interruptions.