Yaz\u0131l\u0131m geli\u015ftirme d\u00fcnyas\u0131nda, \u00f6zellikle modern web uygulamalar\u0131nda, asenkron programlama vazge\u00e7ilmez bir yer tutar. Veritaban\u0131 i\u015flemleri, a\u011f istekleri (API \u00e7a\u011fr\u0131lar\u0131), dosya okuma\/yazma veya zamanlay\u0131c\u0131lar gibi bir\u00e7ok i\u015flem, uygulaman\u0131n ana i\u015f par\u00e7ac\u0131\u011f\u0131n\u0131 (main thread) bloke etmeden arka planda \u00e7al\u0131\u015f\u0131r. Bu sayede kullan\u0131c\u0131 aray\u00fczleri donmaz ve daha ak\u0131c\u0131 bir kullan\u0131c\u0131 deneyimi sunulur. Ancak asenkron kodun do\u011fas\u0131 gere\u011fi, bu t\u00fcr kod bloklar\u0131n\u0131 test etmek senkron kodlara g\u00f6re daha fazla dikkat ve \u00f6zel yakla\u015f\u0131mlar gerektirir. Bir fonksiyonun bir de\u011feri an\u0131nda d\u00f6nd\u00fcrmesi yerine, bir s\u00fcre sonra bir sonu\u00e7 \u00fcretmesi veya bir hata f\u0131rlatmas\u0131 durumu, test \u00e7er\u00e7evelerinin bu bekleme s\u00fcrecini do\u011fru y\u00f6netmesini gerektirir.<\/p>\n
Jest, Facebook taraf\u0131ndan geli\u015ftirilen ve \u00f6zellikle React uygulamalar\u0131 ba\u015fta olmak \u00fczere geni\u015f bir JavaScript projesi yelpazesinde tercih edilen g\u00fc\u00e7l\u00fc ve pop\u00fcler bir test \u00e7er\u00e7evesidir. H\u0131zl\u0131, kullan\u0131m\u0131 kolay ve zengin \u00f6zellik setine sahip olmas\u0131yla \u00f6ne \u00e7\u0131kar. Jest’in en g\u00fc\u00e7l\u00fc yanlar\u0131ndan biri de asenkron kodlar\u0131 test etme konusundaki yetenekleridir. Bu makalede, Jest kullanarak asenkron JavaScript kodlar\u0131n\u0131 nas\u0131l etkin bir \u015fekilde test edebilece\u011fimizi, farkl\u0131 yakla\u015f\u0131mlar\u0131, en iyi uygulamalar\u0131 ve s\u0131k kar\u015f\u0131la\u015f\u0131lan senaryolar\u0131 detayl\u0131 bir \u015fekilde inceleyece\u011fiz.<\/p>\n
Jest ile asenkron testlere dalmadan \u00f6nce, JavaScript’teki asenkron programlama paradigmalar\u0131n\u0131 anlamak \u00f6nemlidir.<\/p>\n
Asenkron JavaScript’in ilk ve en temel yakla\u015f\u0131mlar\u0131ndan biri callback fonksiyonlar\u0131d\u0131r. Bir asenkron i\u015flem tamamland\u0131\u011f\u0131nda \u00e7a\u011fr\u0131lacak olan bir fonksiyonu parametre olarak ge\u00e7irme prensibine dayan\u0131r.<\/p>\n
function fetchData(callback) {\n setTimeout(() => {\n callback(null, 'Veri ba\u015far\u0131yla al\u0131nd\u0131!');\n }, 1000);\n}\n\nfetchData((error, data) => {\n if (error) {\n console.error(error);\n } else {\n console.log(data); \/\/ \"Veri ba\u015far\u0131yla al\u0131nd\u0131!\"\n }\n});<\/code><\/pre>\nCallback’ler basit durumlar i\u00e7in yeterli olsa da, i\u00e7 i\u00e7e ge\u00e7mi\u015f asenkron i\u015flemler (“callback hell”) kodun okunabilirli\u011fini ve y\u00f6netilebilirli\u011fini zorla\u015ft\u0131rabilir.<\/p>\n
Promise’ler<\/h3>\n
ES6 ile birlikte hayat\u0131m\u0131za giren Promise’ler, callback hell sorununa modern bir \u00e7\u00f6z\u00fcm sunmu\u015ftur. Bir Promise, asenkron bir i\u015flemin nihai sonucunu (ba\u015far\u0131l\u0131 ya da ba\u015far\u0131s\u0131z) temsil eden bir nesnedir. \u00dc\u00e7 ana durumu vard\u0131r:
\n* Pending (Beklemede):<\/strong> \u0130\u015flem hen\u00fcz tamamlanmam\u0131\u015ft\u0131r.
\n* Fulfilled\/Resolved (Ba\u015far\u0131l\u0131):<\/strong> \u0130\u015flem ba\u015far\u0131yla tamamland\u0131 ve bir de\u011fer d\u00f6nd\u00fcrd\u00fc.
\n* Rejected (Reddedildi):<\/strong> \u0130\u015flem bir hata ile sonu\u00e7land\u0131.<\/p>\nPromise’ler, .then()<\/code>, .catch()<\/code> ve .finally()<\/code> metotlar\u0131 ile zincirlenebilir bir yap\u0131 sunar.<\/p>\nfunction fetchDataPromise() {\n return new Promise((resolve, reject) => {\n setTimeout(() => {\n const success = true; \/\/ Sim\u00fclasyon: Ba\u015far\u0131l\u0131 veya ba\u015far\u0131s\u0131z\n if (success) {\n resolve('Veri Promise ile ba\u015far\u0131yla al\u0131nd\u0131!');\n } else {\n reject('Veri Promise ile al\u0131namad\u0131!');\n }\n }, 1000);\n });\n}\n\nfetchDataPromise()\n .then(data => console.log(data))\n .catch(error => console.error(error))\n .finally(() => console.log('\u0130\u015flem tamamland\u0131.'));<\/code><\/pre>\nAsync\/Await: Modern ve Okunabilir Yakla\u015f\u0131m<\/h3>\n
ES2017 ile gelen async\/await<\/code> s\u00f6zdizimi, Promise’ler \u00fczerine in\u015fa edilmi\u015f sentaktik bir \u015fekerdir. Asenkron kodu senkron gibi yazma olana\u011f\u0131 sunarak okunabilirli\u011fi b\u00fcy\u00fck \u00f6l\u00e7\u00fcde art\u0131r\u0131r.
\n* async<\/code> anahtar kelimesi, bir fonksiyonun asenkron oldu\u011funu ve her zaman bir Promise d\u00f6nd\u00fcrece\u011fini belirtir.
\n* await<\/code> anahtar kelimesi ise yaln\u0131zca async<\/code> fonksiyonlar i\u00e7inde kullan\u0131labilir ve bir Promise’in \u00e7\u00f6z\u00fclmesini (resolve veya reject olmas\u0131n\u0131) bekler. await<\/code> kullan\u0131ld\u0131\u011f\u0131nda, Promise \u00e7\u00f6z\u00fclene kadar fonksiyonun y\u00fcr\u00fct\u00fclmesi duraklat\u0131l\u0131r ve Promise \u00e7\u00f6z\u00fcld\u00fc\u011f\u00fcnde de\u011ferini d\u00f6nd\u00fcr\u00fcr veya bir hata f\u0131rlat\u0131r.<\/p>\nasync function fetchDataAsync() {\n return new Promise((resolve) => {\n setTimeout(() => {\n resolve('Veri async\/await ile ba\u015far\u0131yla al\u0131nd\u0131!');\n }, 1000);\n });\n}\n\nasync function processData() {\n try {\n const data = await fetchDataAsync();\n console.log(data); \/\/ \"Veri async\/await ile ba\u015far\u0131yla al\u0131nd\u0131!\"\n } catch (error) {\n console.error(error);\n } finally {\n console.log('Async\/await i\u015flemi tamamland\u0131.');\n }\n}\n\nprocessData();<\/code><\/pre>\nasync\/await<\/code>, g\u00fcn\u00fcm\u00fczde asenkron JavaScript kodlar\u0131 yazmak i\u00e7in tercih edilen en modern ve okunabilir yakla\u015f\u0131md\u0131r.<\/p>\nJest’in Asenkron Test Yakla\u015f\u0131mlar\u0131<\/h2>\n
Jest, yukar\u0131da bahsedilen t\u00fcm asenkron programlama paradigmalar\u0131n\u0131 destekler ve test etmeyi kolayla\u015ft\u0131r\u0131r. \u0130\u015fte Jest’in sundu\u011fu temel yakla\u015f\u0131mlar:<\/p>\n
Promise D\u00f6nd\u00fcrmek<\/h3>\n
Jest, bir test fonksiyonundan bir Promise d\u00f6nd\u00fcr\u00fcld\u00fc\u011f\u00fcnde, o Promise’in \u00e7\u00f6z\u00fclmesini veya reddedilmesini otomatik olarak bekler. Promise ba\u015far\u0131l\u0131 olursa test ge\u00e7er, reddedilirse test ba\u015far\u0131s\u0131z olur. Bu, Promise tabanl\u0131 asenkron kodlar\u0131 test etmenin en temel ve yayg\u0131n yollar\u0131ndan biridir.<\/p>\n
Ba\u015far\u0131l\u0131 Promise’leri Test Etmek<\/h4>\n\/\/ myModule.js\nfunction fetchData() {\n return new Promise(resolve => {\n setTimeout(() => resolve('peanut butter'), 100);\n });\n}\n\n\/\/ myModule.test.js\ntest('the data is peanut butter', () => {\n return fetchData().then(data => {\n expect(data).toBe('peanut butter');\n });\n});<\/code><\/pre>\nBu \u00f6rnekte, fetchData<\/code> fonksiyonu bir Promise d\u00f6nd\u00fcr\u00fcyor. Jest, bu Promise’in \u00e7\u00f6z\u00fclmesini bekleyecek ve .then()<\/code> blo\u011fundaki expect<\/code> ifadesi \u00e7al\u0131\u015ft\u0131ktan sonra testin tamamland\u0131\u011f\u0131n\u0131 anlayacakt\u0131r.<\/p>\nReddedilen Promise’leri Test Etmek<\/h4>\n
Bir Promise’in hata ile sonu\u00e7land\u0131\u011f\u0131 durumlar\u0131 test etmek i\u00e7in .catch()<\/code> blo\u011funu kullan\u0131r\u0131z. Ancak burada \u00f6nemli bir nokta var: Jest’in bir Promise’in reddedilmesini bekledi\u011fini ve testin ba\u015far\u0131s\u0131z olmamas\u0131n\u0131 sa\u011flamak i\u00e7in expect.assertions(n)<\/code> kullanmak iyi bir pratiktir. Bu, .catch()<\/code> blo\u011funun ger\u00e7ekten \u00e7al\u0131\u015ft\u0131\u011f\u0131ndan ve i\u00e7inde en az bir assertion’\u0131n (beklenti) ger\u00e7ekle\u015fti\u011finden emin olmam\u0131z\u0131 sa\u011flar. Aksi takdirde, Promise reddedilmezse veya .catch()<\/code> blo\u011fu bir \u015fekilde atlan\u0131rsa, test ba\u015far\u0131yla tamamlanm\u0131\u015f gibi g\u00f6r\u00fcnebilir (\u00e7\u00fcnk\u00fc herhangi bir hata f\u0131rlat\u0131lmaz).<\/p>\n\/\/ myModule.js\nfunction fetchError() {\n return new Promise((resolve, reject) => {\n setTimeout(() => reject('error'), 100);\n });\n}\n\n\/\/ myModule.test.js\ntest('the fetch fails with an error', () => {\n expect.assertions(1); \/\/ En az 1 assertion'\u0131n \u00e7al\u0131\u015faca\u011f\u0131n\u0131 belirtiriz\n return fetchError().catch(e => expect(e).toMatch('error'));\n});<\/code><\/pre>\nAsync\/Await ile Test Etmek<\/h3>\n
async\/await<\/code> s\u00f6zdizimi, asenkron testleri yazmay\u0131 daha da kolayla\u015ft\u0131r\u0131r ve okunabilirli\u011fi art\u0131r\u0131r. Jest, async<\/code> anahtar kelimesiyle tan\u0131mlanm\u0131\u015f test fonksiyonlar\u0131n\u0131 otomatik olarak tan\u0131r ve i\u00e7indeki await<\/code> ifadelerinin tamamlanmas\u0131n\u0131 bekler.<\/p>\nBa\u015far\u0131l\u0131 Durumlar\u0131 async\/await<\/code> ile Test Etmek<\/h4>\n\/\/ myModule.js (ayn\u0131 fetchData fonksiyonu)\nfunction fetchData() {\n return new Promise(resolve => {\n setTimeout(() => resolve('peanut butter'), 100);\n });\n}\n\n\/\/ myModule.test.js\ntest('the data is peanut butter with async\/await', async () => {\n const data = await fetchData();\n expect(data).toBe('peanut butter');\n});\n\ntest('the data is peanut butter with async\/await and .resolves', async () => {\n await expect(fetchData()).resolves.toBe('peanut butter');\n});<\/code><\/pre>\nawait expect(promise).resolves.toBe(value)<\/code> kullan\u0131m\u0131, Promise’in ba\u015far\u0131l\u0131 bir \u015fekilde \u00e7\u00f6z\u00fclmesini ve belirli bir de\u011feri d\u00f6nd\u00fcrmesini bekledi\u011fimizi a\u00e7\u0131k\u00e7a belirtir. Bu, hata y\u00f6netimi yapmadan ba\u015far\u0131l\u0131 senaryolar\u0131 test etmek i\u00e7in \u00e7ok temiz bir yoldur.<\/p>\nHata Durumlar\u0131n\u0131 async\/await<\/code> ile Test Etmek<\/h4>\nHata durumlar\u0131n\u0131 async\/await<\/code> ile test ederken, try...catch<\/code> blo\u011funu kullanabilir veya Jest’in \u00f6zel e\u015fle\u015ftiricisi .rejects<\/code>‘i tercih edebiliriz. .rejects<\/code> kullan\u0131m\u0131 genellikle daha okunabilir ve pratiktir.<\/p>\n\/\/ myModule.js (ayn\u0131 fetchError fonksiyonu)\nfunction fetchError() {\n return new Promise((resolve, reject) => {\n setTimeout(() => reject('error'), 100);\n });\n}\n\n\/\/ myModule.test.js\ntest('the fetch fails with an error using async\/await and try\/catch', async () => {\n expect.assertions(1);\n try {\n await fetchError();\n } catch (e) {\n expect(e).toMatch('error');\n }\n});\n\ntest('the fetch fails with an error using async\/await and .rejects', async () => {\n await expect(fetchError()).rejects.toMatch('error');\n});<\/code><\/pre>\n.rejects<\/code> e\u015fle\u015ftiricisi, beklenen Promise’in reddedilmesini ve belirtilen hata mesaj\u0131n\u0131 veya hata nesnesini i\u00e7ermesini sa\u011flar. Bu y\u00f6ntem, try...catch<\/code> blo\u011funa g\u00f6re daha \u00f6zl\u00fcd\u00fcr ve genellikle tercih edilir.<\/p>\ndone()<\/code> Callback Kullan\u0131m\u0131 (Eski Yakla\u015f\u0131m ve \u00d6zel Durumlar)<\/h3>\nJest’in asenkron testler i\u00e7in sundu\u011fu bir di\u011fer y\u00f6ntem de done()<\/code> callback’idir. E\u011fer test fonksiyonunuz bir Promise d\u00f6nd\u00fcrm\u00fcyorsa veya async<\/code> olarak i\u015faretlenmemi\u015fse, Jest testin ne zaman bitti\u011fini bilemez. Bu durumda, test fonksiyonunuza bir done<\/code> arg\u00fcman\u0131 ekleyebilir ve asenkron i\u015fleminiz tamamland\u0131\u011f\u0131nda bu done()<\/code> fonksiyonunu \u00e7a\u011f\u0131rarak Jest’e testin bitti\u011fini bildirebilirsiniz.<\/p>\nNe \u0130\u015fe Yarar?<\/h4>\n
done()<\/code> callback’i, \u00f6zellikle Promise tabanl\u0131 olmayan (\u00f6rne\u011fin, sadece callback tabanl\u0131) asenkron kodlar\u0131 test ederken veya belirli olay dinleyicilerinin tetiklenmesini beklerken kullan\u0131\u015fl\u0131d\u0131r.<\/p>\n\/\/ myModule.js\nfunction fetchDataWithCallback(callback) {\n setTimeout(() => {\n callback('lemon');\n }, 100);\n}\n\n\/\/ myModule.test.js\ntest('the data is lemon (with done callback)', done => {\n function callback(data) {\n try {\n expect(data).toBe('lemon');\n done(); \/\/ Testin bitti\u011fini Jest'e bildirir\n } catch (error) {\n done(error); \/\/ Hata durumunda Jest'e hatay\u0131 bildirir\n }\n }\n\n fetchDataWithCallback(callback);\n});<\/code><\/pre>\nNeden Genellikle Ka\u00e7\u0131n\u0131lmal\u0131?<\/h4>\n
done()<\/code> callback’i, Promise’ler ve async\/await<\/code> varken genellikle \u00f6nerilmez \u00e7\u00fcnk\u00fc:
\n1. Unutulma Riski:<\/strong> done()<\/code>‘\u0131 \u00e7a\u011f\u0131rmay\u0131 unutursan\u0131z, Jest testin tamamlanmas\u0131n\u0131 sonsuza kadar bekler ve sonunda bir zaman a\u015f\u0131m\u0131 hatas\u0131 verir.
\n2. Okunabilirlik:<\/strong> Promise zincirleri veya async\/await<\/code> yap\u0131s\u0131 genellikle daha temiz ve okunabilirdir.
\n3. Hata Y\u00f6netimi:<\/strong> Hata durumlar\u0131nda done(error)<\/code> \u00e7a\u011f\u0131rmak gerekirken, Promise’ler hatalar\u0131 do\u011fal olarak yayar ve async\/await<\/code> ile try...catch<\/code> bu durumu daha zarif y\u00f6netir.<\/p>\nNe Zaman Kullan\u0131labilir?<\/h4>\n
Nadiren de olsa, baz\u0131 eski k\u00fct\u00fcphanelerle \u00e7al\u0131\u015f\u0131rken veya Promise’lere d\u00f6n\u00fc\u015ft\u00fcr\u00fclmesi zor olan, saf callback tabanl\u0131 veya olay odakl\u0131 asenkron senaryolarda done()<\/code> kullanmak gerekebilir. Ancak m\u00fcmk\u00fcn oldu\u011funca Promise d\u00f6nd\u00fcrme veya async\/await<\/code> kullanma yakla\u015f\u0131m\u0131n\u0131 tercih etmelisiniz.<\/p>\nJest’in Asenkron E\u015fle\u015ftiricileri (Matchers)<\/h2>\n
Jest, asenkron Promise’leri test etmek i\u00e7in \u00f6zel e\u015fle\u015ftiriciler sunar. Bu e\u015fle\u015ftiriciler, Promise’in \u00e7\u00f6z\u00fclme veya reddedilme durumunu daha okunakl\u0131 ve g\u00fcvenli bir \u015fekilde kontrol etmenizi sa\u011flar.<\/p>\n
.resolves<\/code><\/h3>\n.resolves<\/code> e\u015fle\u015ftiricisi, bir Promise’in ba\u015far\u0131yla \u00e7\u00f6z\u00fclmesini ve belirli bir de\u011ferle sonu\u00e7lanmas\u0131n\u0131 bekledi\u011finizi belirtir. Bu e\u015fle\u015ftiriciyi await expect()<\/code> ile birlikte kullanmal\u0131s\u0131n\u0131z.<\/p>\n\/\/ myModule.js\nfunction getUserName(id) {\n return new Promise((resolve, reject) => {\n setTimeout(() => {\n if (id === 1) {\n resolve('Alice');\n } else {\n reject('User not found');\n }\n }, 50);\n });\n}\n\n\/\/ myModule.test.js\ntest('getUserName resolves to Alice for id 1', async () => {\n await expect(getUserName(1)).resolves.toBe('Alice');\n});<\/code><\/pre>\n.rejects<\/code><\/h3>\n.rejects<\/code> e\u015fle\u015ftiricisi, bir Promise’in bir hata ile reddedilmesini bekledi\u011finizi belirtir. Bu e\u015fle\u015ftiriciyi de await expect()<\/code> ile birlikte kullanmal\u0131s\u0131n\u0131z.<\/p>\n\/\/ myModule.test.js\ntest('getUserName rejects with \"User not found\" for id 2', async () => {\n await expect(getUserName(2)).rejects.toBe('User not found');\n});\n\ntest('getUserName rejects with an Error instance for invalid id', async () => {\n function getUserError(id) {\n return new Promise((resolve, reject) => {\n setTimeout(() => {\n if (id === 1) {\n resolve('Alice');\n } else {\n reject(new Error('Invalid user ID'));\n }\n }, 50);\n });\n }\n await expect(getUserError(2)).rejects.toBeInstanceOf(Error);\n await expect(getUserError(2)).rejects.toHaveProperty('message', 'Invalid user ID');\n});<\/code><\/pre>\n.rejects<\/code> ile birlikte toBeInstanceOf<\/code>, toThrow<\/code>, toMatch<\/code> gibi di\u011fer e\u015fle\u015ftiricileri de kullanabilirsiniz.<\/p>\nZaman Tabanl\u0131 Asenkron \u0130\u015flemleri Test Etmek<\/h2>\n
setTimeout<\/code>, setInterval<\/code>, clearTimeout<\/code>, clearInterval<\/code> gibi zamanlay\u0131c\u0131 fonksiyonlar\u0131, asenkron JavaScript’in \u00f6nemli bir par\u00e7as\u0131d\u0131r. Bu t\u00fcr fonksiyonlar\u0131 i\u00e7eren kodlar\u0131 test etmek, genellikle ger\u00e7ek zaman\u0131 beklemek istemedi\u011fimiz i\u00e7in zorlay\u0131c\u0131 olabilir. Jest, bu durumu jest.useFakeTimers()<\/code> ile \u00e7\u00f6z\u00fcme kavu\u015fturur.<\/p>\njest.useFakeTimers()<\/code><\/h3>\nBu fonksiyon, JavaScript’in yerle\u015fik zamanlay\u0131c\u0131lar\u0131n\u0131 Jest’in kendi “sahte” zamanlay\u0131c\u0131lar\u0131yla de\u011fi\u015ftirir. Bu sayede, testlerinizin ger\u00e7ek zaman\u0131 beklemesine gerek kalmaz ve zaman\u0131 manuel olarak ileri sarabilirsiniz.<\/p>\n
jest.advanceTimersByTime()<\/code> ve jest.runAllTimers()<\/code><\/h3>\n* jest.advanceTimersByTime(ms)<\/code>: Zaman\u0131 belirtilen milisaniye kadar ileri sarar ve bu s\u00fcre i\u00e7inde planlanm\u0131\u015f t\u00fcm zamanlay\u0131c\u0131lar\u0131 \u00e7al\u0131\u015ft\u0131r\u0131r.
\n* jest.runAllTimers()<\/code>: Zaman\u0131 olabilecek en ileri noktaya sarar ve bekleyen t\u00fcm zamanlay\u0131c\u0131lar\u0131 (setTimeout, setInterval) an\u0131nda \u00e7al\u0131\u015ft\u0131r\u0131r.
\n* jest.runOnlyPendingTimers()<\/code>: Sadece o an i\u00e7in bekleyen zamanlay\u0131c\u0131lar\u0131 \u00e7al\u0131\u015ft\u0131r\u0131r, ileriye d\u00f6n\u00fck yeni zamanlay\u0131c\u0131lar olu\u015fturulsa bile onlar\u0131 \u00e7al\u0131\u015ft\u0131rmaz.<\/p>\n\u00d6rnek: Debounce Fonksiyonu Testi<\/h4>\n
Bir debounce<\/code> fonksiyonu, belirli bir s\u00fcre i\u00e7inde art arda \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda, sadece son \u00e7a\u011fr\u0131n\u0131n belirli bir gecikmeden sonra \u00e7al\u0131\u015fmas\u0131n\u0131 sa\u011flar. Bu, kullan\u0131c\u0131 giri\u015fi gibi durumlarda performans\u0131 art\u0131rmak i\u00e7in yayg\u0131n olarak kullan\u0131l\u0131r.<\/p>\n\/\/ utils.js\nfunction debounce(func, delay) {\n let timeout;\n return function(...args) {\n const context = this;\n clearTimeout(timeout);\n timeout = setTimeout(() => func.apply(context, args), delay);\n };\n}\n\n\/\/ utils.test.js\ndescribe('debounce', () => {\n beforeEach(() => {\n jest.useFakeTimers(); \/\/ Sahte zamanlay\u0131c\u0131lar\u0131 etkinle\u015ftir\n });\n\n afterEach(() => {\n jest.runOnlyPendingTimers(); \/\/ Bekleyen t\u00fcm zamanlay\u0131c\u0131lar\u0131 temizle\n jest.useRealTimers(); \/\/ Ger\u00e7ek zamanlay\u0131c\u0131lara geri d\u00f6n\n });\n\n test('should debounce the function call', () => {\n const func = jest.fn();\n const debouncedFunc = debounce(func, 1000);\n\n debouncedFunc();\n debouncedFunc();\n debouncedFunc(); \/\/ \u00dc\u00e7 kez \u00e7a\u011fr\u0131ld\u0131\n\n \/\/ Hen\u00fcz zaman ge\u00e7medi\u011fi i\u00e7in func \u00e7a\u011fr\u0131lmam\u0131\u015f olmal\u0131\n expect(func).not.toHaveBeenCalled();\n\n jest.advanceTimersByTime(500); \/\/ 500ms ileri sar\n expect(func).not.toHaveBeenCalled(); \/\/ Hala \u00e7a\u011fr\u0131lmam\u0131\u015f olmal\u0131\n\n jest.advanceTimersByTime(500); \/\/ Toplamda 1000ms ileri sar\u0131ld\u0131\n expect(func).toHaveBeenCalledTimes(1); \/\/ Sadece bir kez \u00e7a\u011fr\u0131lm\u0131\u015f olmal\u0131\n\n \/\/ Yeni bir \u00e7a\u011fr\u0131 yap\u0131p tekrar test edelim\n debouncedFunc();\n jest.advanceTimersByTime(1000);\n expect(func).toHaveBeenCalledTimes(2);\n });\n});<\/code><\/pre>\nBu \u00f6rnekte, jest.useFakeTimers()<\/code> sayesinde setTimeout<\/code> fonksiyonunu manuel olarak kontrol edebiliyoruz. jest.advanceTimersByTime()<\/code> ile zaman\u0131 istedi\u011fimiz kadar ileri sararak, debounce<\/code> fonksiyonunun do\u011fru \u00e7al\u0131\u015ft\u0131\u011f\u0131n\u0131, yani belirli bir gecikmeden sonra sadece bir kez \u00e7a\u011fr\u0131ld\u0131\u011f\u0131n\u0131 do\u011frulayabiliyoruz. beforeEach<\/code> ve afterEach<\/code> bloklar\u0131nda fake timer’lar\u0131 etkinle\u015ftirip devre d\u0131\u015f\u0131 b\u0131rakmak, testlerin izole kalmas\u0131n\u0131 sa\u011flar.<\/p>\nAsenkron \u0130\u015flemleri Taklit Etmek (Mocking)<\/h2>\n
Testlerde, d\u0131\u015f ba\u011f\u0131ml\u0131l\u0131klar\u0131 (API’ler, veritabanlar\u0131, harici servisler vb.) ger\u00e7ek haliyle kullanmak yerine taklit etmek (mocking), testlerin daha h\u0131zl\u0131, g\u00fcvenilir ve izole olmas\u0131n\u0131 sa\u011flar. Jest, asenkron fonksiyonlar\u0131 taklit etmek i\u00e7in g\u00fc\u00e7l\u00fc ara\u00e7lar sunar.<\/p>\n
Neden Mocking Yapar\u0131z?<\/h3>\n
* \u0130zolasyon:<\/strong> Testin sadece kendi birimini test etmesini sa\u011flamak.
\n* H\u0131z:<\/strong> Ger\u00e7ek a\u011f istekleri veya veritaban\u0131 sorgular\u0131 yava\u015f olabilir.
\n* Kontrol:<\/strong> D\u0131\u015f servislerin her zaman istedi\u011fimiz yan\u0131t\u0131 vermedi\u011fi durumlar\u0131 sim\u00fcle etmek.
\n* Maliyet:<\/strong> Baz\u0131 API \u00e7a\u011fr\u0131lar\u0131 maliyetli olabilir.<\/p>\njest.fn()<\/code><\/h3>\njest.fn()<\/code> ile basit taklit fonksiyonlar\u0131 olu\u015fturabiliriz. Bu fonksiyonlar, ka\u00e7 kez \u00e7a\u011fr\u0131ld\u0131klar\u0131, hangi arg\u00fcmanlarla \u00e7a\u011fr\u0131ld\u0131klar\u0131 gibi bilgileri kaydeder.<\/p>\nmockResolvedValue()<\/code> ve mockRejectedValue()<\/code><\/h3>\nBu metotlar, bir taklit fonksiyonunun Promise d\u00f6nd\u00fcren asenkron bir i\u015flemi sim\u00fcle etmesi i\u00e7in kullan\u0131l\u0131r.
\n* mockResolvedValue(value)<\/code>: Taklit fonksiyonunun \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda, Promise’in belirtilen value<\/code> ile ba\u015far\u0131l\u0131 bir \u015fekilde \u00e7\u00f6z\u00fclmesini sa\u011flar.
\n* mockRejectedValue(error)<\/code>: Taklit fonksiyonunun \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda, Promise’in belirtilen error<\/code> ile reddedilmesini sa\u011flar.<\/p>\n\u00d6rnek: API \u00c7a\u011fr\u0131s\u0131n\u0131 Taklit Etmek (fetch<\/code> veya axios<\/code>)<\/h4>\nBir kullan\u0131c\u0131 listesi getiren bir servisimiz oldu\u011funu varsayal\u0131m. Bu servisin ger\u00e7ek bir API’ye istek att\u0131\u011f\u0131n\u0131 d\u00fc\u015f\u00fcnelim.<\/p>\n
\/\/ userService.js\nimport axios from 'axios';\n\nasync function getUsers() {\n const response = await axios.get('https:\/\/api.example.com\/users');\n return response.data;\n}\n\n\/\/ userService.test.js\nimport axios from 'axios';\nimport { getUsers } from '.\/userService';\n\n\/\/ axios'u taklit ediyoruz\njest.mock('axios');\n\ndescribe('getUsers', () => {\n test('should fetch users successfully', async () => {\n const mockUsers = [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }];\n \n \/\/ axios.get \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda belirli bir Promise'i \u00e7\u00f6zmesini sa\u011fl\u0131yoruz\n axios.get.mockResolvedValue({ data: mockUsers });\n\n const users = await getUsers();\n expect(users).toEqual(mockUsers);\n expect(axios.get).toHaveBeenCalledWith('https:\/\/api.example.com\/users');\n });\n\n test('should handle fetch error', async () => {\n const errorMessage = 'Network Error';\n \n \/\/ axios.get \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda bir Promise'i hata ile reddetmesini sa\u011fl\u0131yoruz\n axios.get.mockRejectedValue(new Error(errorMessage));\n\n await expect(getUsers()).rejects.toThrow(errorMessage);\n expect(axios.get).toHaveBeenCalledWith('https:\/\/api.example.com\/users');\n });\n});<\/code><\/pre>\nBu \u00f6rnekte, jest.mock('axios')<\/code> ile axios<\/code> mod\u00fcl\u00fcn\u00fc tamamen taklit ediyoruz. Ard\u0131ndan axios.get.mockResolvedValue<\/code> ve axios.get.mockRejectedValue<\/code> kullanarak, getUsers<\/code> fonksiyonunun i\u00e7indeki axios.get<\/code> \u00e7a\u011fr\u0131s\u0131n\u0131n ger\u00e7ek bir a\u011f iste\u011fi yapmas\u0131n\u0131 engelliyor ve istedi\u011fimiz yan\u0131tlar\u0131 d\u00f6nd\u00fcrmesini sa\u011fl\u0131yoruz. Bu, testlerimizin h\u0131zl\u0131 ve d\u0131\u015f ba\u011f\u0131ml\u0131l\u0131klardan ar\u0131nm\u0131\u015f olmas\u0131n\u0131 garanti eder.<\/p>\nmockImplementation()<\/code><\/h3>\nDaha karma\u015f\u0131k taklit senaryolar\u0131 i\u00e7in mockImplementation()<\/code> kullan\u0131labilir. Bu metot, taklit fonksiyonunun ne yapaca\u011f\u0131n\u0131 tam olarak kontrol etmenizi sa\u011flar.<\/p>\n\/\/ userService.test.js (mockImplementation \u00f6rne\u011fi)\nimport axios from 'axios';\nimport { getUsers } from '.\/userService';\n\njest.mock('axios');\n\ntest('should return different data based on arguments with mockImplementation', async () => {\n axios.get.mockImplementation((url) => {\n if (url === 'https:\/\/api.example.com\/users') {\n return Promise.resolve({ data: [{ id: 1, name: 'Charlie' }] });\n }\n if (url === 'https:\/\/api.example.com\/products') {\n return Promise.resolve({ data: [{ id: 101, name: 'Laptop' }] });\n }\n return Promise.reject(new Error('Not Found'));\n });\n\n const users = await getUsers(); \/\/ getUsers fonksiyonu https:\/\/api.example.com\/users'\u0131 \u00e7a\u011f\u0131r\u0131yor\n expect(users).toEqual([{ id: 1, name: 'Charlie' }]);\n\n \/\/ Farkl\u0131 bir URL ile \u00e7a\u011fr\u0131ld\u0131\u011f\u0131nda ne olaca\u011f\u0131n\u0131 test etmek i\u00e7in\n const getProducts = async () => {\n const response = await axios.get('https:\/\/api.example.com\/products');\n return response.data;\n };\n const products = await getProducts();\n expect(products).toEqual([{ id: 101, name: 'Laptop' }]);\n});<\/code><\/pre>\nAsenkron Testlerde En \u0130yi Uygulamalar<\/h2>\n
Asenkron testler yazarken verimlili\u011fi ve g\u00fcvenilirli\u011fi art\u0131rmak i\u00e7in baz\u0131 en iyi uygulamalar \u015funlard\u0131r:<\/p>\n
async\/await<\/code> Tercih Edin<\/h3>\nM\u00fcmk\u00fcn oldu\u011funca async\/await<\/code> kullan\u0131n. Promise tabanl\u0131 kodlar\u0131 test etmenin en okunakl\u0131, modern ve y\u00f6netilebilir yoludur. Callback tabanl\u0131 kodlar\u0131 bile bir Promise’e sarmalayarak async\/await<\/code> ile test edebilirsiniz.<\/p>\nexpect.assertions(n)<\/code> Kullan\u0131n<\/h3>\n\u00d6zellikle try...catch<\/code> bloklar\u0131 i\u00e7inde veya Promise’in reddedilme durumlar\u0131n\u0131 test ederken expect.assertions(n)<\/code> kullanmak, testin bekledi\u011finiz say\u0131da assertion’\u0131 ger\u00e7ekten \u00e7al\u0131\u015ft\u0131rd\u0131\u011f\u0131ndan emin olman\u0131z\u0131 sa\u011flar. Bu, asenkron bir kodun beklenmedik bir \u015fekilde ba\u015far\u0131s\u0131z olmas\u0131 durumunda testin yanl\u0131\u015fl\u0131kla “ge\u00e7ti” olarak i\u015faretlenmesini engeller.<\/p>\ndone()<\/code> ve Promise\/Async-Await’i Kar\u0131\u015ft\u0131rmay\u0131n<\/h3>\nBir test fonksiyonu hem bir Promise d\u00f6nd\u00fcr\u00fcyor hem de done()<\/code> callback’ini \u00e7a\u011f\u0131r\u0131yorsa, Jest karars\u0131z davran\u0131\u015flar sergileyebilir. Her test i\u00e7in tek bir asenkron y\u00f6netim stratejisi se\u00e7in: ya Promise d\u00f6nd\u00fcr\u00fcn (veya async<\/code> kullan\u0131n) ya da done()<\/code> callback’ini kullan\u0131n, ikisini birden de\u011fil.<\/p>\nTestleri \u0130zole Edin (beforeEach<\/code>, afterEach<\/code>)<\/h3>\nbeforeEach<\/code> ve afterEach<\/code> kancalar\u0131n\u0131 kullanarak her testten \u00f6nce gerekli kurulumlar\u0131 yap\u0131n (\u00f6rne\u011fin, sahte zamanlay\u0131c\u0131lar\u0131 etkinle\u015ftirme) ve her testten sonra temizlik i\u015flemlerini (\u00f6rne\u011fin, sahte zamanlay\u0131c\u0131lar\u0131 s\u0131f\u0131rlama, taklitleri temizleme) ger\u00e7ekle\u015ftirin. Bu, testlerin birbirini etkilemesini engeller ve g\u00fcvenilirli\u011fi art\u0131r\u0131r.<\/p>\ndescribe('My Async Module', () => {\n beforeEach(() => {\n jest.useFakeTimers();\n \/\/ Di\u011fer kurulumlar (\u00f6rne\u011fin, taklitleri s\u0131f\u0131rlama)\n });\n\n afterEach(() => {\n jest.runOnlyPendingTimers();\n jest.useRealTimers();\n jest.clearAllMocks(); \/\/ T\u00fcm taklit \u00e7a\u011fr\u0131lar\u0131n\u0131 temizle\n });\n\n \/\/ Testler buraya gelecek\n});<\/code><\/pre>\nJest’in Varsay\u0131lan Zaman A\u015f\u0131m\u0131 (Timeout) Ayarlar\u0131n\u0131 Anlay\u0131n<\/h3>\n
Jest’in varsay\u0131lan olarak her test i\u00e7in 5 saniyelik bir zaman a\u015f\u0131m\u0131 s\u00fcresi vard\u0131r. E\u011fer asenkron i\u015fleminiz bu s\u00fcreden daha uzun s\u00fcr\u00fcyorsa, Jest testi ba\u015far\u0131s\u0131z kabul eder. Bu s\u00fcreyi jest.setTimeout(ms)<\/code> ile global olarak veya test('...', () => {...}, ms)<\/code> ile her test i\u00e7in ayr\u0131 ayr\u0131 ayarlayabilirsiniz.<\/p>\ntest('this test takes a long time', async () => {\n await someLongRunningAsyncOperation();\n}, 10000); \/\/ Bu test i\u00e7in 10 saniye zaman a\u015f\u0131m\u0131<\/code><\/pre>\nAnlaml\u0131 Test \u0130simleri Kullan\u0131n<\/h3>\n
Asenkron testler, senkron testlere g\u00f6re biraz daha karma\u015f\u0131k olabilece\u011finden, test isimlerinin neyi test etti\u011fini ve hangi senaryoyu kapsad\u0131\u011f\u0131n\u0131 a\u00e7\u0131k\u00e7a belirtmesi \u00f6nemlidir. \u00d6rne\u011fin, “should resolve with correct data” veya “should reject with a specific error message”.<\/p>\n
Sonu\u00e7<\/h2>\n
Asenkron programlama, modern JavaScript uygulamalar\u0131n\u0131n kalbinde yer al\u0131r ve bu kodlar\u0131 do\u011fru bir \u015fekilde test etmek, uygulaman\u0131n g\u00fcvenilirli\u011fini ve s\u00fcrd\u00fcr\u00fclebilirli\u011fini sa\u011flamak i\u00e7in kritik \u00f6neme sahiptir. Jest, Promise’ler, async\/await<\/code> ve done()<\/code> callback’i gibi \u00e7e\u015fitli yakla\u015f\u0131mlarla asenkron kodlar\u0131 test etmek i\u00e7in kapsaml\u0131 ve kullan\u0131m\u0131 kolay bir \u00e7er\u00e7eve sunar.<\/p>\nBu makalede ele ald\u0131\u011f\u0131m\u0131z gibi, async\/await<\/code> kullan\u0131m\u0131 en modern ve okunabilir yakla\u015f\u0131md\u0131r. Jest’in .resolves<\/code> ve .rejects<\/code> gibi \u00f6zel e\u015fle\u015ftiricileri, Promise tabanl\u0131 testleri daha da kolayla\u015ft\u0131r\u0131r. jest.useFakeTimers()<\/code> ile zaman tabanl\u0131 asenkron i\u015flemleri kontrol alt\u0131na almak ve jest.mock()<\/code> ile d\u0131\u015f ba\u011f\u0131ml\u0131l\u0131klar\u0131 taklit etmek, testlerinizi daha h\u0131zl\u0131, izole ve g\u00fcvenilir hale getirir.<\/p>\nEn iyi uygulamalar\u0131 takip ederek \u2013 async\/await<\/code>‘i tercih etmek, expect.assertions(n)<\/code> kullanmak, testleri izole etmek ve anlaml\u0131 test isimleri vermek \u2013 asenkron testlerinizi daha verimli bir \u015fekilde yazabilir ve uygulaman\u0131z\u0131n kalitesini art\u0131rabilirsiniz. Jest’in sundu\u011fu bu g\u00fc\u00e7l\u00fc ara\u00e7larla, asenkron kodlar\u0131n\u0131z\u0131n beklendi\u011fi gibi \u00e7al\u0131\u015ft\u0131\u011f\u0131ndan emin olabilir, b\u00f6ylece daha sa\u011flam ve hatas\u0131z uygulamalar geli\u015ftirebilirsiniz.<\/body><\/p>\n","protected":false},"excerpt":{"rendered":"Jest ile Asenkron Testler: Modern Yakla\u015f\u0131mlar ve En \u0130yi Uygulamalar\nGiri\u015f\nYaz\u0131l\u0131m geli\u015ftirme d\u00fcnyas\u0131nda, \u00f6zellikle modern web uygulamalar\u0131","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"csco_page_header_type":"","csco_page_load_nextpost":"","csco_page_subscribe_form":"","csco_page_contact_form":"","footnotes":""},"categories":[1],"tags":[],"class_list":{"0":"post-32978","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-genel","7":"cs-entry","8":"cs-video-wrap"},"yoast_head":"\nJest ile Asenkron Testler: Modern Yakla\u015f\u0131mlar ve En \u0130yi Uygulamalar - 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