使用 mockito 模拟返回带有通配符的泛型的方法 [英] mocking a method that return generics with wildcard using mockito

问题描述

我使用的是 mockito 1.9.5.我有以下代码:

公共类 ClassA {公共列表getMyInterfaces() {返回空；}公共静态无效 testMock() {列表接口 = 新的 ArrayList<>();ClassA classAMock = mock(ClassA.class);当(classAMock.getMyInterfaces()).thenReturn(interfaces);}

我收到 thenReturn(interfaces) 的编译错误说:

"类型中的方法 thenReturn(List)OngoingStubbing)"

但是，当我使用mockito 的thenAnswer 方法时，我没有收到错误消息.谁能告诉我这是怎么回事?为什么在使用 thenReturn 方法时会出现错误?当ClassA由第三方提供且无法修改时，是否有其他方法可以解决此问题?

解决方案

EDIT :从 Mockito 1.10.x 开始，嵌入在类中的泛型类型现在被 Mockito 用于深层存根.IE.

公共接口 A<T extends Observer &可比性>{列表bList();T观察者()；}B b = deep_stubbed.bList().iterator().next();//返回一个 B 的模拟；mockito 记得 A 返回 B 的列表观察者 o = deep_stubbed.observer();//mockito 可以发现 T 超类型是 Observer可比性c = deep_stubbed.observer();//或者 T 实现了 Comparable

Mockito 尽力获取编译器嵌入的类型信息，但是当擦除适用时，mockito 除了返回 Object 的模拟之外什么也做不了.

<小时>

原文:与 Mockito 相比，泛型的问题更多.对于泛型，您应该阅读 Angelika Langer 写的关于它们的内容.对于当前主题，即通配符，请阅读此部分.>

但简而言之，您可以使用 Mockito 的其他语法来帮助您解决当前情况:

doReturn(interfaces).when(classAMock).getMyInterfaces();

或者使用 BDD 别名:

willReturn(interfaces).given(classAMock).getMyInterfaces();

尽管如此，您可以编写更通用的包装器.这将有助于未来的开发者使用相同的 3rd 方 API.

<小时>

附带说明:您不应该模拟您不拥有的类型，它会导致许多错误和问题.相反，您应该有一些包装器.例如，DAO 和存储库代表了这样的想法，人们将模拟 DAO 或存储库接口，而不是 JDBC/JPA/hibernate 的东西.有很多关于此的博客文章:

• 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?

解决方案

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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