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Home Interviews What are mocking frameworks you’ve used with .NET? Examples? – MindStick
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ICSM Computer
ICSM Computer 17 Jun 2025
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Mocking frameworks are essential in .NET unit testing for isolating dependencies and simulating behavior of external components like services, databases, or APIs. Here are some of the most popular mocking frameworks used with .NET, along with examples:

1. Moq (Most Popular)

Moq is a widely used and easy-to-learn mocking library for .NET.

Installation

dotnet add package Moq

Example – Mocking a service

Interface:

public interface IUserService
{
    string GetUserName(int id);
}

Test using Moq:

var mock = new Mock<IUserService>();
mock.Setup(s => s.GetUserName(1)).Returns("Anna");

var controller = new UsersController(mock.Object);
var result = controller.GetUserName(1); // Should return "Anna"

Assert.Equal("Anna", result);

2. NSubstitute

A simpler and more intuitive alternative to Moq.

Installation

dotnet add package NSubstitute

Example:

var userService = Substitute.For<IUserService>();
userService.GetUserName(1).Returns("Anna");

var result = userService.GetUserName(1);
Assert.Equal("Anna", result);

3. FakeItEasy

Very readable syntax; good for newcomers.

Installation

dotnet add package FakeItEasy

Example:

var service = A.Fake<IUserService>();
A.CallTo(() => service.GetUserName(1)).Returns("Anna");

var result = service.GetUserName(1);
Assert.Equal("Anna", result);

4. JustMock (Telerik)

  • Supports mocking non-virtual members, static, and sealed classes.
  • Has both free and paid editions.

Example:

var service = Mock.Create<IUserService>();
Mock.Arrange(() => service.GetUserName(1)).Returns("Anna");

Assert.Equal("Anna", service.GetUserName(1));

5. Microsoft Fakes (only in Visual Studio Enterprise)

  • Can mock static and sealed classes.
  • Available in VS Enterprise only.
  • Uses shim and stub concepts.

Summary Table

Framework Syntax Style Can Mock Sealed/Static Popularity Notes
Moq Fluent (only interfaces/virtual) ⭐⭐⭐⭐⭐ Most common, widely used
NSubstitute Natural Yes ⭐⭐⭐⭐ Simple and clean syntax
FakeItEasy Natural Yes ⭐⭐⭐⭐ Very readable
JustMock Fluent (paid version) ⭐⭐⭐ Paid version powerful
Microsoft Fakes Stub/Shim Yes ⭐⭐ Only in VS Enterprise
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