public void afterTaskCompletion(MigrationRunnable task) {
        if (migrateTaskCount.decrementAndGet() < 0) {
            throw new IllegalStateException();
        }
    }
@Test(expected = IllegalStateException.class)
    public void test_migrateTaskCount_notDecremented_belowZero() {
        migrationQueue.afterTaskCompletion(mock(MigrationRunnable.class));
    }