question: public static void sleep ( long millis ) { if ( mockSleepQueue == null ) { sleepUninterruptibly ( millis , TimeUnit . MILLISECONDS ) ; } else { try { boolean isMultiPass = mockSleepQueue . take ( ) ; rollMockClockMillis ( millis ) ; if ( isMultiPass ) mockSleepQueue . offer ( true ) ; } catch ( InterruptedException e ) { } } }
target:  Sleep for a span of time, or mock sleep if enabled 