improve unit test robustness
improve unit test robustness

joseph-hurtado/KVOController,modocache/KVOController,sanojnambiar/KVOController,Lt-Red/KVOController,1yvT0s/KVOController,wujizhidao/KVOController,kjiwu/KVOController,lookingstars/KVOController,clg0118/KVOController,target/KVOController,pengleelove/KVOController,dbachrach/KVOController,caoer/KVOController,tipbit/KVOController,godLoveLucifer/KVOController,SuPair/KVOController,gank0326/KVO,SanChain/KVOController,Pingco/KVOController,codepython/KVOController,Eveian/KVOController,HqRaining78/KVOController,yaoxiaoyong/KVOController,acerbetti/KVOController,CQXfly/KVOController