WebUSB testing relies on the WebUSB Testing API which must be provided by browsers under test.
In this test suite resources/usb-helpers.js detects and triggers
the API to be loaded as needed.
The Chromium implementation is provided by
../resources/chromium/webusb-test.js using MojoJS.
Tests with the "-manual" suffix do not use the test-only interface and expect a real hardware device to be connected. The specific characteristics of the device are described in each test.