libusbg: tests: Add tests for gadget strings enum
libusbg: tests: Add tests for gadget strings enum

Test recently added functions using usbg_gadget_str enum.

Signed-off-by: Pawel Szewczyk <1691dcf8dab804b326e5e4b9ab228a1c3b23a2f2@samsung.com>
Reviewed-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg