問題描述
我使用的是 mockito 1.9.5.我有以下代碼:
公共類 ClassA {公共列表getMyInterfaces() {返回空值；}公共靜態(tài)無效testMock(){列出<我的界面>接口 = 新的 ArrayList<>();ClassA classAMock = mock(ClassA.class);when(classAMock.getMyInterfaces()).thenReturn(interfaces);}我得到一個編譯錯誤 thenReturn(interfaces) 說:
"類型中的thenReturn(List)方法OngoingStubbing<List<capture#1-of ?擴展我的接口>>不適用于論點(列表<MyInterface>)" 但是，當(dāng)我使用 mockito 的 thenAnswer 方法時，我沒有收到錯誤消息.誰能告訴我發(fā)生了什么事?為什么我在使用 thenReturn 方法時會收到錯誤消息?當(dāng) ClassA 由第三方提供且無法修改時，是否有其他方法可以解決此問題?
編輯:從 Mockito 1.10.x 開始，嵌入在類中的泛型類型現(xiàn)在被 Mockito 用于深度存根.IE.
公共接口 A<T 擴展 Observer &可比Mockito 盡力獲取編譯器嵌入的類型信息，但是當(dāng)應(yīng)用擦除時，mockito 只能返回 Object 的模擬.
原創(chuàng):嗯，這更多是泛型的問題，而不是 Mockito 的問題.對于泛型，您應(yīng)該閱讀 Angelika Langer 在它們上寫的內(nèi)容.對于當(dāng)前主題，即通配符，請閱讀此部分.p>
但簡而言之，您可以使用 Mockito 的其他語法來幫助您解決當(dāng)前的情況:
doReturn(interfaces).when(classAMock).getMyInterfaces();或者使用 BDD 別名:
willReturn(interfaces).given(classAMock).getMyInterfaces();盡管如此，您可以編寫更通用友好的包裝器.這將有助于未來的開發(fā)人員使用相同的第 3 方 API.
<小時>附帶說明:您不應(yīng)該模擬您不擁有的類型，這可能會導(dǎo)致許多錯誤和問題.相反，你應(yīng)該有一些包裝.例如 DAO 和存儲庫就代表了這樣的想法，人們將模擬 DAO 或存儲庫接口，而不是 JDBC/JPA/hibernate 的東西.有很多關(guān)于此的博客文章:
- http://davesquared.net/2011/04/dont-mock-types-you-dont-own.html
- http://blog.8thlight.com/eric-smith/2011/10/27/thats-not-yours.html
- https://web.archive.org/web/20140923101818/http://freshbrewedcode.com/derekgreer/2012/04/01/tdd-best-practices-dont-mock-others/
- ...
I'm using mockito 1.9.5. I have the following code:
public class ClassA {
public List<? extends MyInterface> getMyInterfaces() {
return null;
}
public static void testMock() {
List<MyInterface> interfaces = new ArrayList<>();
ClassA classAMock = mock(ClassA.class);
when(classAMock.getMyInterfaces()).thenReturn(interfaces);
}
I get a compilation error for the thenReturn(interfaces) saying:
"The method thenReturn(List<capture#1-of ? extends MyInterface>) in the type
OngoingStubbing<List<capture#1-of ? extends MyInterface>> is not applicable for the arguments
(List<MyInterface>)"
However, when I use the thenAnswer method of mockito, I don't get the error. Can anyone tell me what's going on? Why do I get the error when I use the thenReturn method?
Is there any other way to solve this problem when ClassA is provided by a 3rd party and cannot be modified?
EDIT : Starting from Mockito 1.10.x, generics types that are embedded in the class are now used by Mockito for deep stubs. ie.
public interface A<T extends Observer & Comparable<? super T>> {
List<? extends B> bList();
T observer();
}
B b = deep_stubbed.bList().iterator().next(); // returns a mock of B ; mockito remebers that A returns a List of B
Observer o = deep_stubbed.observer(); // mockito can find that T super type is Observer
Comparable<? super T> c = deep_stubbed.observer(); // or that T implements Comparable
Mockito tries its best to get type information that the compiler embeds, but when erasure applies, mockito cannot do anything but return a mock of Object.
Original : Well that's more of an issue with generics than with Mockito. For generics, you should read what Angelika Langer wrote on them. And for the current topic, i.e. wildcards, read this section.
But for short, what you could use is the other syntax of Mockito to help with your current situation :
doReturn(interfaces).when(classAMock).getMyInterfaces();
Or with the BDD aliases :
willReturn(interfaces).given(classAMock).getMyInterfaces();
Nevertheless, you could write wrappers that are more generic friendly. That will help future developers working with same 3rd party API.
As a side note: you shouldn't mocks type you don't own, it can lead to many errors and issues. Instead you should have some wrapper. DAO and repositories for example represent such idea, one will mock the DAO or repository interface, but not the JDBC / JPA / hibernate stuff. There are many blog posts about that:
- http://davesquared.net/2011/04/dont-mock-types-you-dont-own.html
- http://blog.8thlight.com/eric-smith/2011/10/27/thats-not-yours.html
- https://web.archive.org/web/20140923101818/http://freshbrewedcode.com/derekgreer/2012/04/01/tdd-best-practices-dont-mock-others/
- ...
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