CC3351: Does Wi-Fi adaptive testing require entering any specific mode?

Hello,

There is no special mode needed for adaptivity testing. A normal connection to an AP will enable adaptivity mode by default. 

Just connect to the AP as a station and begin running traffic from the station to the AP.

The CC3351 passed ETSI certification including the adaptivity test, you can see the cert reports here: https://www.ti.com/drr/opn/SIMPLELINK-CC33XX-REPORTS 

Regards,

Jonathan