Bit width used by the tests are entirely within the range of a long, so there is nothing stopping one from using a long to represent everything.

Speaking of which, 80% of the kata is covered via java.util.BitSet. This kata could use more novelty.

The description does not mention (or rather, the kata author does not know) how capacity should be changed under various operations.

It's never described either what to do if two Bits are of different length. Initial code contains some validation, but never on this part.

Initial code contains a partially written solution of dubious code quality. Please put only the stub as initial code.

There are no random tests.

Could you please tell what kill and live methods should do? It's not clear to me.