Cherrypick from R2020a branch which got the new tests.
Attribute read/write test
set.GainChannel0/1 using setAttributeDouble instead of LongLong
Changed RF Bandwidth upper limit to 56MHz, Center Frequency lower limit to 47MHz, set.AttenuationChannel0/1 using setAttributeDouble instead of LongLong
Changed hardwaregain setAttribute to Double instead of LongLong
Add rx manual gain check in AttributeSingleValue
Change GainChannel step from 0.25 to 1
Set EnabledChannels property to [1 2] instead of 2 for rx.
Cherrypick from R2020a branch which got the new tests.