Test tool work as Black- box testing. They could perform software tests without having to set up a real-real scenario, they don’t need to understand how the tool works.
Test tool could be set up the monitor and modify the raw communications that occurs among those million computers(testing networking software)
Test tool could be set up to monitor and modify the raw communications that occurs among those million computer seem white-box skills and knowledge of the low-level protocol to effectively use the tool.