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Can we mock an extension method?

Pentru teste mai mult ca sigur ati folosit un framework petru a face mock pe diferite obiecte. In general am folosit Moq pentru a putea face mock la date. Este destul de usor de folosit, mai jos puteti sa gasiti un exemplu:
Mock<IService> serviceMock = new Mock<IService>();
serviceMock
    .Setup(x=>x.Call(It.IsAny<string>))
    .Returns(()=> new Result());
Mai sus am creat un mock pentru IService, iar in momentul in care se apeleaza metoda Call cu orice parametru de tip string, se returneaza un nou obiect de tip Result.
Nimic deosebit pana acuma. Dar ce se intampla daca vrem sa facem mock la un extension method. Vestea proasta este ca nu se poate face. Majoritatea framework-urilor pentru mock-ing nu suporta aceasta functionalitate.
Cea mai buna solutie este sa refactorizam codul daca putem. Dar exista cazuri cand acest lucru nu il putem face sau extension method nu este declarat de noi si vine dintr-un assembly exterior.
O solutie comuna, care poate sa fie folosita atat pentru aplicatiile .NET classic, Silverlight, WP7, ... este sa injectam actiunea care apeleaza metoda noastra. De exemplu putem sa extragem intr-un Action actiunea care apeleaza extension method, iar aceasta sa fie injectata prin contructor folosind un factory de exemplu. O alta varianta este sa facem un wrapper peste clasa noastra.
Urmatoarea solutie nu functioneaza pe Silverlight din pacate. Ar fi fost nice sa fie suportatat macar in versiunea 5, dar nici o sansa. Solutie se refera la folosirea Microsoft Moles. Prin intermediul acestui framework putem sa inlocuim orice clasa, metoda cu un mole care sa faca ce vrem noi. Un mole, intercepteaza apelul spre o anumita metoda si se poate executa orice alt cod. Putem sa facem mole la orice fel de metoda, atat statica cat si extension method.

Comments

  1. Un extension method nu e decat o metoda statica, deci nu e de mirare ca majoritatea frameworkurilor de mocking care lucreaza cu metode "ortodoxe" nu au cum sa creeze un mock pentru asa ceva..

    Si Moles sau Typemock Isolator pot sa mockuiasca o metoda statica pentru ca se baga cu CLR profiler-ul si rescriu IL-ul, si alte ghidusii de genul.

    ReplyDelete
  2. Partea interesanta este cand ai un proiect Silverlight si nu ai aceste optiuni.
    Daca ar fi sa aleg intre Moles si Moq as alege Moq, dar uneori nu ai de ales, sau in cazul asta numarul de optiuni este egal cu 0.

    ReplyDelete
  3. Da, in cazul acesta daca mocking framework-ul nu are versiune de Silverlight, cam singura optiune e un adapter sau refactoring daca e posibil..

    ReplyDelete
  4. Am ajuns la o solutie asemanatoare. Putin de refactoring, un factory impreuna cu un adaptor. O sa revin maine cu implementarea exacta.

    ReplyDelete

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