我相信斯科特的解决方案在某种程度上是有效的，

但是不使用反射来窥探私有api是一个很好的理由。它现在坏了。

我可以使用委托设置参数

      delegate void MockOutDelegate(string s, out int value);

    public void SomeMethod()
    {
        ....

         int value;
         myMock.Setup(x => x.TryDoSomething(It.IsAny<string>(), out value))
            .Callback(new MockOutDelegate((string s, out int output) => output = userId))
            .Returns(true);
    }

这是来自Moq网站的文档:

// out arguments
var outString = "ack";
// TryParse will return true, and the out argument will return "ack", lazy evaluated
mock.Setup(foo => foo.TryParse("ping", out outString)).Returns(true);


// ref arguments
var instance = new Bar();
// Only matches if the ref argument to the invocation is the same instance
mock.Setup(foo => foo.Submit(ref instance)).Returns(true);

似乎不可能开箱即用。看来有人想要解决问题

请看这个论坛帖子 http://code.google.com/p/moq/issues/detail?id=176

这个问题 用最小订货量验证参考参数的值

对克雷格·塞莱斯特的答案进行了增强，任何人都可以使用它。out参数为IsAny:

public interface IService
{
    void DoSomething(out string a);
}

[TestMethod]
public void Test()
{
    var service = GetService();
    string actualValue;
    service.Object.DoSomething(out actualValue);
    Assert.AreEqual(expectedValue, actualValue);
}

private IService GetService()
{
    var service = new Mock<IService>();
    var anyString = It.IsAny<string>();
    service.Setup(s => s.DoSomething(out anyString))
        .Callback((out string providedString) => 
        {
            providedString = "SomeValue";
        });
    return service.Object;
}

如果你的方法也需要返回一些东西，你也可以使用Returns而不是Callback。

在Billy Jakes awnser的基础上，我用一个out参数做了一个完全动态的模拟方法。我把这个贴在这里给那些觉得有用的人。

// Define a delegate with the params of the method that returns void.
delegate void methodDelegate(int x, out string output);

// Define a variable to store the return value.
bool returnValue;

// Mock the method: 
// Do all logic in .Callback and store the return value.
// Then return the return value in the .Returns
mockHighlighter.Setup(h => h.SomeMethod(It.IsAny<int>(), out It.Ref<int>.IsAny))
  .Callback(new methodDelegate((int x, out int output) =>
  {
    // do some logic to set the output and return value.
    output = ...
    returnValue = ...
  }))
  .Returns(() => returnValue);

这是一个解决方案。

[Test]
public void TestForOutParameterInMoq()
{
  //Arrange
  _mockParameterManager= new Mock<IParameterManager>();

  Mock<IParameter > mockParameter= new Mock<IParameter >();
  //Parameter affectation should be useless but is not. It's really used by Moq 
  IParameter parameter= mockParameter.Object;

  //Mock method used in UpperParameterManager
  _mockParameterManager.Setup(x => x.OutMethod(out parameter));

  //Act with the real instance
  _UpperParameterManager.UpperOutMethod(out parameter);

  //Assert that method used on the out parameter of inner out method are really called
  mockParameter.Verify(x => x.FunctionCalledInOutMethodAfterInnerOutMethod(),Times.Once());

}