what's `Test command format: { 1, '!', 0,0,0, 0,0, 0 }` and how to use it?

[Pro2Factory]

In the HID doc: https://github.com/todbot/blink1/blob/4df2d06215b5c1c9221f3cfd91ef8e550a681e7f/docs/blink1-hid-commands.md?plain=1#L26C7-L26C70

What's that? How to test with it?