How to Write Unit Test for New Code based on Legacy Code.pdf

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1、HowtoWriteUnitTestforNewCodeontopofLegacyCodeJosephYao•UnitTest101•MakeYourCodeTestable•IsolateYourDependency•SuggestionsPleaseReadThisGreatBook!UnitTest101What’sUnitTest?Unittestsistheideathattheyaretestsinisolationofindividualcomponentsofsoftware-MichaelC.FeathersWhyWeneedUnitTest?W

2、hyWeneedUnitTest?WhyWeneedUnitTest?WhyWeneedUnitTest?What’sLegacyCode?Legacycodeissimplycodewithouttests.Withouttestsisbadcode.Itdoesn'tmatterhowwellwrittenitis;itdoesn'tmatterhowprettyorobject-orientedorwell-encapsulateditis.Withtests,wecanchangethebehaviorofourcodequicklyandverifiab

3、ly.Withoutthem,wereallydon'tknowifourcodeisgettingbetterorworse.-MichaelC.FeathersMakeYourCodeTestableHowtoInitializeYourDependencyinNewClassNeedYourCodeLooksLikeThis?publicclassCar{privateEngineengine;publicCar(){engine=newEngine();}publicbooleanisMove(){returnengine.speed()>0?true:f

4、alse;}}YourTestLooksLikeThis?publicclassTestCar{@Testpublicvoidmove(){Carcar=newCar();assertTrue(car.isMove());}}AreyoureallydotheunittestforCar?CodeforCarwithIsolationpublicclassCar{privateIEngineengine;publicCar(IEnginetheEngine){engine=theEngine;}publicbooleanisMove(){returnengine.

5、speed()>0?true:false;}}TestforCarwithIsolationpublicclassTestCar{@Testpublicvoidmove(){IEngineengineMock=newEngineMock(10);Carcar=newCar(engineMock);assertTrue(car.isMove());}}Infact,youdon’tcarehowenginespeediscalculatedMorewaystoInitializeDependencyinUT•SetmethodCar.setEngine(engine

6、Mock);•OveridemethodinSub-classoTestCarisasubclassofCaroCarhasaprotectedmethod(getEngine)togetEngineoTestCarcanoveridethismethodtoprovideaengineMockINeedtoTestaPrivateMethodinNewClassYourCodeLooksLikeThis?publicclassOrder{publicvoidaddItem(Itemitem){if(isValidItem(item)){items.add(ite

7、m);}}privatebooleanisValidItem(Itemitem){morethan500linescode…}}HowcanItesttheprivatemethod?DoesYourClassHavetoomanyResponsibilities?MaybeThisCodeisBetter?publicclassOrder{privateItemValidatorvalidator;publicOrder(ItemValidatortheValidator){validator=theValidator;}publicvoidaddItem(It

8、emite