Question 1

How do I mock a method with out parameters in Moq?

Accepted Answer

Moq has intuitive support for out/ref parameters. Use the Callback or Returns methods with lambda expressions to set output values, as mentioned in the features. For example, mock.Setup(x => x.Method(out It.Ref<int>.IsAny)).Returns(true) handles out parameters seamlessly.

Question 2

Moq vs NSubstitute: which is better for .NET unit testing?

Accepted Answer

Both are popular, but Moq excels with its LINQ-based, type-safe API and strong IntelliSense integration, while NSubstitute offers a more fluent, natural language syntax. Choose Moq if you prioritize refactoring safety and tooling; NSubstitute for a different stylistic preference.

Question 3

Can Moq mock sealed classes?

Accepted Answer

No, Moq cannot mock sealed classes directly because it relies on dynamic proxy generation, which requires inheritance or implementation. You must mock interfaces or use virtual methods in unsealed classes instead.

Question 4

How to verify a method was called exactly once in Moq?

Accepted Answer

Use the Verify method with Times.Once(). For example, mock.Verify(x => x.SomeMethod(), Times.Once()) checks the call count. This is part of Moq's straightforward verification model without record/replay complexity.

Question 5

What's the difference between Mock.Of and new Mock in Moq?

Accepted Answer

Mock.Of uses LINQ to Mocks for concise setup, returning the mocked object directly, ideal for simple cases. new Mock gives a Mock<T> instance for detailed configuration and verification, better for complex scenarios.

Question 6

Does Moq support async methods?

Accepted Answer

Yes, Moq fully supports async methods. Use ReturnsAsync or Setup for methods returning Task or ValueTask, making it easy to mock asynchronous dependencies in modern .NET applications.

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