Description

b := New(0)
b.Set(N)
b.ShiftRight(N) // expect to have the zero bit set, as (2^N) >> N == 1
b.Test(0) // false...

Fix

It seems like an off by one error in ShiftRight. We should empty the set iff the shift distance exceeds the number of top set bit. When the shift distance equals to the top set bit, that is the only bit what is left after the shift.
It also required adjusting one existing test case.