Generate a black line art icon showing an app icon encapsulated within a bubble, to illustrate sandboxing. The app icon should be generic but recognizable, such as a simplified square with rounded corners and a central symbol indicative of functionality (e.g., a cogwheel, a lock). The bubble surrounding it should be represented by a single, continuous line, suggesting isolation and protection. This design must be straightforward and legible, perfectly conveying the idea of an isolated testing en