如何在 thenReturn 函数中返回传递给 Mockito 模拟方法的参数？

Question

这就是我想要实现的目标。

MyClass doSomething =  mock(MyClass.class);
when(doSomething.perform(firstParameter, any(Integer.class), any(File.class)))
    .thenReturn(firstParameter);

基本上我希望模拟类的方法始终返回传递到该方法中的第一个参数。

我尝试过使用ArgumentCaptor，就像这样

ArgumentCaptor<File> inFileCaptor = ArgumentCaptor.forClass(File.class);
MyClass doSomething = mock(MyClass.class);
when(doSomething.perform(inFileCaptor.capture(), any(Integer.class), any(File.class)))
    .thenReturn(firstParameter);

但mockito刚刚失败并出现此错误消息：

No argument value was captured!
You might have forgotten to use argument.capture() in verify()...
...or you used capture() in stubbing but stubbed method was not called.
Be aware that it is recommended to use capture() only with verify()

Examples of correct argument capturing:
    ArgumentCaptor<Person> argument = ArgumentCaptor.forClass(Person.class);
    verify(mock).doSomething(argument.capture());
    assertEquals("John", argument.getValue().getName());

我认为该ArgumentCaptor课程仅适用于verify通话。

那么如何返回测试时传入的第一个参数呢？

Answer 1

您通常使用以下方法执行此操作thenAnswer：

when(doSomething.perform(firstParameter, any(Integer.class), 
             any(File.class)))
    .thenAnswer(new Answer<File>() {
          public File answer(InvocationOnMock invocation) throws Throwable {
        return invocation.getArgument(0);
    }
 };

你可以将其简化为

when(doSomething.perform(firstParameter, any(Integer.class), any(File.class)))
  .thenAnswer(invocation -> invocation.getArgument(0));

Answer 2

你也可以这样做org.mockito.AdditionalAnswers

when(doSomething.perform(eq(firstParameter), any(Integer.class), any(File.class)))
    .thenAnswer(AdditionalAnswers.returnsFirstArg())

@Fred 解决方案也可以用 lambda 编写

when(doSomething.perform(eq(firstParameter), any(Integer.class), any(File.class)))
        .thenAnswer(i->i.getArgument(0));