private IOException recvException = null;
        private boolean connectFails = false;
        private boolean disconnectResult = false;

        @Override
        protected long makeKey(Request request) throws IOException {
            return nextKey++;
        }

        @Override
        protected Long peekKey() throws IOException {
            if (recvException != null) {

                Arguments.of(makeSeq(8), 0, 8, 0), // full copy at index 0
                Arguments.of(makeSeq(10), 2, 5, 3), // middle slice, non-zero dst index
                Arguments.of(makeSeq(4), 4, 0, 0), // zero-length slice at end
                Arguments.of(makeSeq(16), 7, 3, 0), // small slice from middle
                Arguments.of(makeSeq(16), 0, 0, 5) // zero-length with non-zero dst index
        );