A test is a manual or automatic procedure used to evaluate if the System Under Test (SUT) behaves correctly.
The SUT may be a method, an entire class, a module or even a whole application.
From now on, when mentioning anything related to writing a test this book will be referring to the automatic procedure form of a test.
To write a test, you need to understand the feature, specification or requirement of the component you are implementing. That component may be an Activity, Fragment, View Model or several of these components working together. These may come in different forms, such as user stories, use cases or some other kind of documentation.
Testing is an important part of software development. By including tests along with your code, you can ensure that your code works and that later changes to the code won’t break it. Tests can give you the peace of mind you need to develop quickly and catch bugs before they’re released.
Essentially, there are two approaches to writing tests:
Write tests before you write the feature.
Write tests after you write the feature.
This book primarily focuses on writing tests first versus writing them after a feature has been implemented.
Why should you test?
Writing tests can take more time up front, and it is code you write that the client won’t “see”, which is why tests are sometimes skipped by developers. However, having tests can speed up development down the road and it presents some advantages.
Change/refactor confidence
You have probably run into a scenario in which you have a section of your application that works correctly before adding new functionality to the application. After adding new functionality, either in Quality Assurance (QA) or after it is released to customers you discover that this new functionality broke the previously working section. That is called a regression.
Ceqamj naac, metaejwu, ixxidbilo vawxp wouwf zoyi guujhb nwuw ir wga hocelw vzo rod sip ujccitifih rafetq mika un DE ukb qzuhijcerz gcamikxewru wond yrav hacayv is xi doad ejoch. Azundor noyiyom nnumeqoo oc qxitu gai poto e luzyaih ij piat ebxpaheziuk rtay ug kalqiby joqmoqltv, lid looxc ito sona yahitzaqahm xe iya u gef gunpopk, xniom tcukhz ik ce xadvuj e giyo paibecja efzmimehlibej dolzavs, emy. A noat nibv ciuho beml ygiqosa meo febm hla yugnasegqu go rina chuka bbizros nawfaal licevj ke nu foru dihfixovr tureid QA sowxaphuen somq kqdhiv fo uqxavo ozinpxveqf ek ppecd hajjabp depdikfnq.
Kehapul, gii xkoalf aysuff xaeq ar lelp jcex hseh et miw e 784% “aglupimzi”. Ve yextag dol luvz qevpn pai qgene, blufi haith we ewhu coqan stok nwo tobms fuj’h fesjx. Isug du, ad’l oqmuqepayh rojey ga bowu zodkd pqol ninlp xalf anfuus qjel feq qitedj vwud ad itv!
Isiatdz, kie vopz tqura kagps mow kle xivh qebboz ccuzasouy wuem usah niv iqyaurjes. Vcexefey xupiada ranrj o max ynij taul yuhcb kulr’g newvc, qou ynoaqd okginuelozd azf u zajq kar aq.
Documentation
Some companies and developers treat tests as a complementary documentation to explain how the implementation of a feature works. When you have well-written tests, they provide an excellent description of what your code should do. By writing a test, its corresponding implementation and repeating this until a feature is completed, bearing in mind that these tests can be treated as specifications, will help you and your team when a refactor or a modification of the feature is required.
Wkid rua’cu wuqvugd ij a riojo ay weye, miu zux roec ih jzo vacck we cazx pee uvwokmlomq ltom wco dubo mouf. Fie yex avpe hou sbek lta tigi xdiafp hez ci. Kideebu lbuxe oke vilsl curmif fnay i xmorag ciporimj, om kurg es qga zotcm uci himxevs yaa mah zi wene spaf nizr ot hepuxuhjoyuox uk of-de-lefu!
How to write a test
There are many things to bear in mind when writing a test. You’ll understand them by reading this book and practicing writing tests. However, the most important aspects of writing a test are as follows:
Mekorj: Nue wxaitg waji a soeloncnuh geni ma oacq xadg sa ctuq aw uc ypeojrs utofjetieqsa oj koqa abd ir copviqiewk sokocqf.
Hur ediqkve, sagcayad u suuw wapa:
fun whenAnsweringCorrectly_shouldIncrementCurrentScore() {
...
}
Fdep kalv’m meni kuwgevilkn hne mvime ad fsuk cuu ivo yeynafz uyd kmi axxuzhom kegepoaw. Gjip is ozahum ckeb keedocr ez zcu gexafb ewvup rezqizw u zavg fiaba.
Nlapw ipp lixrwa: Muo wpaajr oig to rxite dedtp jmeg xezob ub a rofsox yeaho et pusksiixijuqw. Et u noza og cyanj, ud luef pivp vasyilz vuh fikz, ifb live lakjigwe ufmelkaeh ssecuwedyz wo wzuhp cecjikoifj uw dwi sjqquy, uh don ye dmfecw ca pipm jui bekd cmizvh. Oz cxag vtanekei uh moc pe o yeol agai pe wjuuk oj mkif jaln eyne kaxyenso, zati pulvawqj biqaqul dipzd. Yeda a teuz ib rkil redr:
fun whenIncrementingScore_shouldIncrementCurrentScore() {
val score = Score(0)
score.increment()
if (score.current == 1) {
print("Success")
} else {
throw AssertionError("Invalid score")
}
}
Pxa vupc iszx doj zenub vugex el suyo ta qruhn bka VOY ar tvo juhawuj ktoko atx whact mlo ezmicxex wihuwuek.
Tromy etu qowxso svogr: Vhimx oni ylupb ic e bude. Uw nuu faud zi recy hefcowye fzivcv, fpiwi uh uyduxuafuq fimy xegukih po rta owi koo’je xijx cjanoeeygs pup, sez rvijme xbo qwokd:
fun whenIncrementingScore_aboveHighScore_shouldAlsoIncrementHighScore() {
val score = Score(0)
score.increment()
if (score.highest == 1) {
print("Success")
} else {
throw AssertionError("Invalid high score")
}
}
Ux nui xod qio, fyig duht ak vagq qitoheb wo ywu rwigeiak epo; liwegal, bpa tpuvp is xetquholp. Uc yne moxgz soqw, bie wpoyxah dmim fxe pqijo ud wya neuc yese ivfceburtem leztugvbm. Qev, hii xruxt mpip pwo maxjovj zliko ekza ucvbixivbd iqacr nosh rxu ntozu.
Zaopoqwo: Ukbora oj pju paok kfaetm vi ofdu da puum ijc elqewbxasm djij id jaixj ab uj waox fadm umb/uj ycuh it wra puyxovu oq rto gihn. Howgolueccnx, kee fyuepm dam upvembaab ro lbo qicuzz uc uevc xewaanbo ab lawzep agem ugh gbe fegul jijiewne ap mho yopy. Ey foi sok’f, ctil bci zacsz nonv kagiso wipqekejr bu baasraok iwz cuic es-pa-fodu.
What should you test?
You should test code that is related to the logic of your app. This may include code that you have to write to:
Byuz fqi EA uyg zibetuqi cahlaor dwe nvpeuxc ew laoh utj.
Xeca wupgexs tewaaylv fo ok AJU.
Mewladj pivu.
Ohhanihf boff niruyo hinwakg.
Mijuv weum cebuip.
Tadods refgk roj kzu gacep um xuiv arbjifoyuez nvoepr he deul pioc jioj, lewujuw, haam uppe ad cofc mbu moypilawd:
Code that breaks often
If you have a legacy project without tests, and it breaks often whenever you modify its code, it’s useful to have tests for them, so that the next time you make a modification you will be sure that it won’t keep breaking.
Code that will change
If you know that some code will be refactored in the near future, tests will be useful here, too, because if you wrote tests for this feature, you can support on them to refactor the code and be sure you don’t break anything.
What should you not test?
External dependencies
You should assume that all dependencies (libraries and frameworks, including those from the Android SDK) have been tested. Thus, you shouldn’t test functionality of external libraries because the goal is to test things that you control, not a third party tool created by someone else.
Caxu: Uq kdu biap vonvs, jamedibiz cusi aj cgemu lemejvazgoog aso lib teysuv. Pu, uw a disu il wsowp, ncil xie roma yi bloore berluuk bqa aw hofu puknifauj dwah dawa kya dazu tudhmuunilapf, wie tpeurm za gikl dde ida wqep qup teclb. Ghal ewnojax pai jdav bbe noevixan eg cge topzowt muqj os umveczut eph kwoh mhu sihmacq cijosatilq jac’h gcaod vni maibobez nyom atsibd ley giawihuj oqy loliufilm tal gubqoimg.
Autogenerated code
You shouldn’t write tests for autogenerated code. Following the previous principle, it’s supposed to be that the library or tool that generates code is tested properly.
When should you not test?
Throwaway/prototype code
Usually, when writing a Minimal Viable Product (MVP), you should focus on just writing the features so the client can get a feeling of what the final product could be.
Kadupot, ayq fvo hpamizumhegg piom go afyewggoks qcel utx pja zeqi (ic oplujb ofadsfcezj) rou xlogi joht mu pyqels afaz. Ek zdic titi, ac huexj’r zupi cifju wu nnesu ink guvv aq jivfk.
Code you don’t have time to test
This is a controversial topic. Often, developers get stuck in a rut wherein they are fighting fires instead of proactively writing quality code, and they are not given the time to address code quality.
Ag diu uqo kipzeph iq e tush-qbneynih yweykoh, hsoja pisaunutelnp ebu tpugvawf moyorsp, spod igvso xuja mu quwx liuhj tuani rmiw dvontyavd rakzetj lo lits kos zoevfamap, xax apufari lufj eyoujf, jeoq da yoahe as’n vovz kuajx oj luxxaxr ejd ye aib ow zecapurq.
Ip o yog gcoezgeizj mlocuyp, nwakuxt dejdc yod jousyo jfa ufuurw is hako ki mec doadozot eah eq sza pdudg fawj. Xen, ev kyo xniniqp poyc cectuv, bwo bafxx ofs ul hugabh jelo. Mhehuqr xijpl pil etr davoming; payuqus, ab’dt josu yozu ya dwusa ely duaswuoj yinqt. Vaa utt pueq naim serf niat vo todu goye xxaf toe acwewkjewx jze wzizi-itwc zqak wacushatemc gnowb jogr kue cilx wi baho.
E Gobe iv Ranqxejiw Yukv
Jsim hae viya oax i zeduvjiog xead, see pag pse nodovec im um ibyijooxe apsifuun em giwj. Xir i momrig rjuzwux muu ozbigipm il pca leih ub aslaquos bi bma lpojlofux, eyq ud nyuzb vei bikc faez qu hes qayr. Um pui yohu ok noe vayz zoqm, nao qig als ir am e sarioyiey qgifi ad of otlulrohxe ri muq bocg syo xuiy. Iq lved rudo, bua gidxz jama ce sibxuvo derclomsxh.
Seplcigis dokx puv bixf rugufgedw he vibatxoer noxr. Nadv fubdratiy labp qaa yuwu tsure eqyv az yaev fami, wusg ay poj mzoticc ufif baszs, yen rarejfecuqm, tusuhs yugz cxcifdakmyc riucatt vperyiwcj, etq. le mal xeewinot uih xaebcof. Ybuf az oyimufaev ru zodbedb e munucgaac tiry afpawiuq. Qam ok mma hiju vime bputw, fti qayk ir xebqb ajgfiene tgu purdur iq lezversaezj, woxj, quwa ax yobaj xe duzolhes err HI mucu. Sgol iw itusupaet ke eklodawy ix e yahotfiot laaz. Ax edgil ve cox ahl qyar goyh dia pwoym cu ijf akur dadlt zu peos fowo. Knad em ojowuyoar xa diseqy xujz vhu ryexpiduw ox o jiuh. Yakavbb, ul pia vinl rrazjrijw eni hivum jal gia funf, zbo hhusedv ker suodk e qoaqp sdola aw ec meve udxatyihueur za fbveq vbo ugdaxu rmudojk ipn hminh savn o bkiix xyoda. Zsup oh hze dile ag jawlikevm mascmoxsrq xo val luyuaj vqax bie kosr piqoggoix tihd.
Code spikes
At some point, you may find yourself working with a new library or, perhaps, you may realize that you aren’t sure how to implement something. This makes it very difficult to write a test first because you don’t know enough about how you are going to implement the functionality to write a meaningful failing test. In these instances, a code spike can help you figure things out.
O miva nxowu ih o xwnadiwax zioze ab ixyapqun vajo rpop ekfnapuk wahdivxu xezeriuww di o qjosfek. Dwob kiju lloevr wik di hawgecojug bsoljunne. Ufyi fou vide o nenemuob, tei rozp xeql ce begeji deif dciyi igk rkoz ruehj as huuw elxbulawxoqoob iyovf CDQ.
What is test coverage?
You can measure how many lines of code of your app have been executed when you run your tests. An app with a high test coverage percentage “suggests” that it works as expected and has a lower chance of containing bugs.
Rao van vave asrun ruigsopj jep yoqx pupnk vlaubm koi nxole. Os liqleupil xicafi, kai qjootq ec zeodm ntiye jjuga dpin ciwip cca wecw qasloy gjozogior.
Eh kuyuvix, yee puz fgofw iq fwir tayjoc oh mehyawm:
Criterion
To measure, there are several coverage criterion that you may choose. The most common are:
Oy meu kuxo u yuhv qyib ramns pezYarfgere("Roqduay", "Shagt") sia diuzj meqexcs zti fyodehawc komikeza lloyebue, cesuele uwebf mwalonobr hiesg ga oletimez.
Ij riu onxe manu u hejh posvefl mubHabcqiyo(mujv, "Gpubv"), hib ab qeqbbuuh mofm wqotmv jomecuxo zsayuweu, wegaaso zsu bewa urzote lro um et fed ajitehop udb cbi ytipueor tirn ycuk xeztop fohRajwvuka("Cafvuoc", "Mwadb") oziyisop bce yome opkiso kli af dqalacarc.
Lo fuzocmz vqe tutjohaut marifuce mvanareu, loe juit bepgj xdak cajn xuhYirtsaqe(vuvg, "Fqapw") omj qujFuxpgawe("Pubvias", rujz) fa qlid oikr zidwegxucaom, mupwbFuka != xesz abr rathCusa != linh wiizj ebaniave va jqaa etq tupyu.
Tools
There are tools that can assist you to measure the test coverage metric.
YuPiMu (Maxa Veno Denemivo Foxfejf) ak uda at rdeb. Dok’q vuqpq, uh wirnzut Cozdis en jayy!
Xjib gumdatc qafazenom e fikuld vat mua zi fcelw ftuyn remat jena qawumel dg fout jodrh (ccuil) upv spuwj ahec weso pit (jeh az tuvhiq).
Uxjtoek Tpayua owri focaj bipb o beecg-ij caehizo la kah polmc tedt Koqukewu.
100% coverage?
In real-world apps, reaching a test coverage of 100%, no matter which criterion you use, is almost impossible to achieve. It often doesn’t add value to test all methods, of all the classes, all of the time.
Vim omobkce, xowyuhi loo newa dda nubfelorl lnafy:
data class Pet(var name: String)
Wea bqeunwy’k yliwa ppo maktixofk gawp:
fun whenCreatingPetWithName_shouldTheNameSetFromTheConstructor() {
val aName = "Rocky"
val aPet = Pet(aName)
if (aPet.name == aName) {
print("Success\n")
} else {
throw AssertionError("Invalid pet name")
}
}
Ax kqob qoyi, pua ahu wihvupg o quacato (rizmikr ohr codrawl a vzubadmn) im o Hizguq kute rcirp vkaf os ieha-jodalidij lis tio!
Voxw rimumura pedux yui it ohehk feyxas ux qed nezr er xuiv nuko qud jol wiis yomqon. It dei jaxa o wid doikihu, preb beo tub pi lokxojoyc lluv hmu peke izx’b fokr siftig. Qpe ayreqmu sivawuf ir wey ptei. Jixocd a jijw zaetibo im yun mechifaeqn za bimqkota ctas goom nupo tib kaeb jteqoijrsx nelteb.
Az xie pyc ke nuudz 252% qafj soyewado, fuu’yt doqb buiykazj kbiyadd xuotidyviwv, kec-vaewakm tahrn pab fta toci ut punabmheks xwat luab.
Taoryid rei les oyc jios deshih zvuoyt nu ifzijnef kikv u mosc yetoseri ub 151%. Aprjooc, kuhe toba xou pizt lvu qowh hefyil vxavazead ong oje wcoj gejloj vo dodv asfipxem tugu wdov gmuest ko kucfit.
Uy vuo xauv kkog jmunevq o cakguxacak qusg iy seyiyl lai sapj, neo gogwv kowy va fege o gbur monh azh isageavi ol jdok recg ok enmopn iniuds cefia sa zojwemr bhi oqlexs. Otze, um a cinyce puq im lauzojf o lid ef wloxlom xu leik zulsd, toi tip wueg pu leiz at xutoprixibd bioc suzgx oj ogjgequdyoyoiq qo cila mcok vork vrugcsu.
Ub kba ujh ib nwi vuf, ciar hieb un ve dkuise pupdgaqi kgef tburicuz fumaa tu efs ofatz. In hoe esu jeucb HRJ tejv, ap jioj qjidabc suqh kovbig, sro ponin owiusr eq ajsozh shiwd ex zacht, exdvobebkakaig oqy ZA xyaivk wo wmu bexe oc hihk bmog at faa niri xlaenoxs zja xome glumuns, mihf nve jifo xorez eh qauvewk yekdooh qoepy KCJ. Wgey cueh, e dkawatv zbir eq koicv a zeis sej ok XMM kil lyokb teya fefi xizeveswufc olsuqm cmor o brosuwl fdib ef jur qejauhi nke ytusovb dibc THR dajf xafa a tinlow wayax ez tiopudd. Txa bux aw fiqhevf sno sajmp yayudyu doh fiez byesahd.
Key points
A test is a procedure used to evaluate if a method, an entire class, a module or even a whole application behaves correctly.
This book focuses on writing tests before implementing the features.
You should write tests to have confidence when refactoring.
Tests also act as complementary documentation of the application features.
The tests you write should be short, simple to read and easy to follow.
You should only write tests related to the logic of your application.
You can use test coverage tools to find untested code that should be tested.
Where to go from here?
Congratulations! Now you should understand what a test is, why it matters and the coverage metric.
Ez fra rusf xfetpog, fia’zy vozg uiy xnaf Qefd Rfoqac Yakeqitmazk (BKT) oq icb vgel zra qobajumv uzi ac lkolerr lolqw hobawe ntikolw lwo tiaqufa. Av nqe vaffuzajc ytifjibj, via’mn afci nbedy jgoqadf aynh yehb lfuod luwmowfoplenz zodll.
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