How to Mock Out and Ref Parameters with Moq?

Moq: Handling Out and Ref Parameters

Mocking out and ref parameters with Moq presents unique challenges due to the generic nature of Action<t></t>. Let's explore how to address this.

For out parameters, Moq provides a direct solution. The setup mirrors the method call, capturing the output value:

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

[TestMethod]
public void TestOutParameter()
{
    var serviceMock = new Mock<IService>();
    string expectedValue = "value";
    serviceMock.Setup(s => s.DoSomething(out expectedValue));

    string actualValue;
    serviceMock.Object.DoSomething(out actualValue);
    Assert.AreEqual(expectedValue, actualValue);
}

Moq effectively captures expectedValue during setup and uses it when the mocked method is called.

Unfortunately, Moq doesn't offer a similarly elegant solution for ref parameters. The Moq QuickStart guide (https://www.php.cn/link/a77054e9d6c3fb75907aed15140ca1e6) provides more comprehensive guidance on advanced usage scenarios, including alternative approaches for handling ref parameters which might involve using callbacks or custom matchers.

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