public void prepareForRebalance() {
            nextExpectedNumStableAssignments = numStableAssignments.get() + 1;
        }
Saves the current number of stable rebalances so that we can tell when the next stable assignment has been
reached. This should be called once for every invocation of {@link #waitForNextStableAssignment(long)},
before the rebalance-triggering event.
streams/src/test/java/org/apache/kafka/streams/integration/utils/IntegrationTestUtils.java