Mockito returnsFirstArg() 不适用于通用的第一个参数

Question

EDIT: I've finally created an issue on mockito github project.

我正在尝试使用 Mockito AdditionalAnswers.returnsFirstArg 功能将接口 RoomGeneralService 的类型化方法 getNameElement 模拟为 return 第一个参数：

模拟接口:

interface PrimaryKeyElement<T> {
   public String getNameElement(T primaryKey);
}

interface RoomGeneralService extends PrimaryKeyElement<String> {
   // ...
}

我的测试（注意进口）

import static org.mockito.AdditionalAnswers.returnsFirstArg;
import static org.mockito.Matchers.any;
import static org.mockito.Matchers.anyString;
import static org.mockito.Mockito.when;

@RunWith(PowerMockRunner.class)
public class SampleTest {

   @Mock
   RoomGeneralService roomGeneralService;

   @Test
   public void testFoo() throws Exception {
      when(roomGeneralService.getNameElement(anyString())).thenAnswer(returnsFirstArg());
      //...
   }
}

我也尝试过其他组合，但到目前为止没有成功：

when(roomGeneralService.getNameElement(Matchers.<String>any())).thenAnswer(returnsFirstArg());
doAnswer(returnsFirstArg()).when(roomGeneralService.getNameElement(anyString()));
doReturn(returnsFirstArg()).when(roomGeneralService.getNameElement(anyString()));

收到错误:

The reason for this error can be : 1. The wanted argument position is incorrect. 2. The answer is used on the wrong interaction.

Position of the wanted argument is 0 and the possible argument indexes for this method are : [0] Object

解决方法：

我知道我可以创建自己的答案，事实上，如果不使用 returnFirstArg() 我会这样做，它工作正常：

when(roomGeneralService.getNameElement(anyString())).thenAnswer(new Answer<String>() {
   @Override
   public String answer(InvocationOnMock invocation) throws Throwable {
      return (String) invocation.getArguments()[0];
   }
});

但我会像在我的其余测试中一样使用 returnFirstArg()（测试看起来更干净），并且如果方法 getNameElement 会收到 String，模拟工作正常取而代之的是 T arg.

感谢您的帮助。

Answer 1

Mockito 似乎不够聪明，无法推断参数类型将绑定到参数化子接口中的 String。

您可以覆盖子接口中的方法

interface RoomGeneralService extends PrimaryKeyElement<String> {
    @Override
    public String getNameElement(String primaryKey);
}

Mockito 无需猜测。它会清楚地看到 String 作为存根方法的参数类型。

Answer 2

终于决定开issue了(#1071) on mockito github project and it has been fixed in version 2.8.29 (See the official changelog)感谢Mockito团队这么快就解决了！

引用@ChristianSchwarz，这里有一个问题解释：

Mockito checks if the argument type is compatible with the return type to make a misuse ot the API as soon as posible visible. In this case the argument-type Object is inferred from the generic type T, due to type erasure. Since Object is not a subtype of String Mockito throws the exception you see.

Solution: The issue can by fixed by inferring the argument-type of the actual argument-instance. In case the argument-type is a primitive or the arg is null Mockito must fallback and use the type provided by method signature.

Mockito returnsFirstArg() 不适用于通用的第一个参数

Mockito returnsFirstArg() doesn't work with generic first arg

java

mocking

mockito

powermock

matcher