NSubstitute Introduction and Why I like it

Recently I am heavily learning Test Driven Development and Domain Driven design. As you know With TDD you need to have a mocking libraries. So after doing on research on internet they are three libraries available in Microsoft.NET development world which are quite mature.

  1. Rhino Mocks
  2. NSubstitute
  3. Moq
I have gone through all of above three and then After doing research and I choose NSubstitute.

Why I Choose NSubstitute:

Following are the reasons why I have chosen NSubstitute.

  1. It is super easy to use. I don’t have to write very complex lamda expressions to mock objects.
  2. It works really fine with all framework of Test Driven Development
  3. As it is super easy to use you need to write very less code to mock objects.
  4. With other Visual Studio plugins like Resharper, Telerik Justcode its works perfectly and they are able to generate code for the same.
  5. It’s got fluent syntax and very easy to understand.
  6. It’s perfect for some one who is not mature enough for Test Driven Development.

NSubstitute - Basic Introduction:

NSubstitute is relatively a new kid on the block as compare to other two mocking libraries. It’s is a open source project hosted on github. You can find all the information related to NSubsitute via following site.


It’s also available on NuGet and You can install it via Nuget via following command.


So what’s we are waiting for Let’s create a demo application to see how it’s works. I am going to create a console application to demonstrate this.


I am also going to Add a Test Project to Run my test created with Help of NSubstitute.


Now I’m going to create person interface like below.
namespace NSubstituteBasicDemo
    public interface IPerson
        string GetFullName(string firstName,string lastName);
And same way I am going to create implementation of IPerson interface like below.
namespace NSubstituteBasicDemo
    public class Person : IPerson
        public string GetFullName(string firstName, string lastName)
            return string.Format("{0} {1}", firstName, lastName);
Now it’s time to write Test and for that we need to add nuget package for NSubstitute in test project.


Once we are done I have written following code to write a test for Person class.
using Microsoft.VisualStudio.TestTools.UnitTesting;
using NSubstitute;
using NSubstituteBasicDemo;

namespace NSubstituteTest
    public class PersonTest
        public void ToCheck_Whether_Person_FullName_Work_Or_Not()
            //Creating Substiute for person
            var person = Substitute.For<IPerson>();
            //Adding a return value
            person.GetFullName("Jalpesh", "Vadgama").Returns("Jalpesh Vadgama");

            //Asserting to check whether its fine or not
            Assert.AreEqual("Jalpesh Vadgama", person.GetFullName("Jalpesh", "Vadgama"));

Now when you run this Test it’s work perfectly.


That’s it. Hope you like it. Stay tuned for more.

You can find complete source code of this blog post at -https://github.com/dotnetjalps/NSubstituteExamples


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