Mocking using MOQ framework

In this article we will understand various mocking setups using Moq framework. Basically those setups help during the of unit testing of an application. If you have experience in unit testing then you are probably aware of these concepts. We know that mocking is an operation where we mimic the original operation with our custom or fake operation. At the time of application development, we sometimes see that one component is dependent on another component and we cannot wait until the completion of the dependent object.

In this situation, the concept of mocking comes into the picture. The mock object will mimic the original object, so that we can carry on with the development process. There are many mocking frameworks on the market which we can use for our mock object creation. Moq is one of them. It is free and simple to use. In this article we will use Moq as our mocking framework. At the time of the mock setup there might be different situations which we need to implement during unit test configuration. In this example we will understand a few of the important setups of Moq framework.

At first, give the reference of Moq framework to your application. Once you give the reference, it will show in the reference folder of the solution, as shown below.

So, let’s start with the first configuration.

Returns statement to return value

We can setup the expected return value to a function. In this example we will setup the Hello() function using a mock object and then we will setup so that after the execution of the Hello() function it will always return "true." Here, true is a primitive type value. If we are in need we can return our custom complex type too. Please notice that we have declared the Hello() function as virtual, because Moq demands that. The function should defined as virtual when we are going to mock a concrete implementation. Have a look at the below code.

namespace TestMVC

{

    public class TestClass

    {

        public virtual Boolean Hello()

        {

            throw new Exception();

        }

    }

    [TestClass]

    public class MVCUnitTest

    {

        [TestMethod]

        public void MockAlways()

        {

            var mock = new Mock<TestClass>();

            mock.Setup(x => x.Hello()).Returns(true);

            Assert.AreEqual(mock.Object.Hello(), true);

        }

    }

}

Perform certain task after execution of certain function

This is another very important setup. Sometime it’s needed to perform certain operations after the completion of other operations or after the execution of some function. For example, we want to count the number of times of a function execution, and will assess those times in order to influence our decisions. In this situation we can setupcallback() in time of mock. Here is a sample example.

 [TestClass]

    public class MVCUnitTest

    {

        [TestMethod]

        public void MockAlways()

        {

            string status = "";

            var mock = new Mock<Service>();

            mock.Setup(x => x.CallService()).Returns(true).Callback(() => {

                //Do some other stuff

                status = "FunctionCalled";

            });

            var consumer = new ServiceConsumer(mock.Object);

            Assert.AreEqual(consumer.Execute(), true);

            if (status == "FunctionCalled")

            {

                //perform other task when finish the first

            }

        }

    }

Once it completes the execution of the CallService() function, it immediately will execute callback and perform some other operation. In this example just we are setting some variable value and it might check further to take decisions in other steps.

Return multiple values sequentially from mocked function

This is another important setup where the mocked function (I mean the function setup associated with mock object) will return different values per each call. Here is a simple implementation:

using System;

using ConsoleApp;

using Microsoft.VisualStudio.TestTools.UnitTesting;

using Moq;

using ConsoleApp;

using System.Collections.Generic;

namespace TestMVC

{

    public class TestClass

    {

        public virtual Boolean ReturnSequence()

        {

            throw new Exception();

        }

    }

    [TestClass]

    public class MVCUnitTest

    {

        [TestMethod]

        public void MockAlways()

        {

            var mock = new Mock<TestClass>();

           

            //First Return True then false

            mock.SetupSequence(x => x.ReturnSequence())

                .Returns(true)

                .Returns(false);

            Assert.AreEqual(mock.Object.ReturnSequence(), true);

            Assert.AreEqual(mock.Object.ReturnSequence(), false);

        }

    }

}

In this example we have used multiple Returns() statements. The first time it will return true and the next time it will return false. Here is the output and we are seeing that the test is getting passed, as we expected.

Throws exception in second time

There might be certain situations where we want a configuration when the mocked function will return a value the first time, but in if called a second time it will throw an exception. In this example the function will return true at the first time and in the second call it will throw an exception.

namespace TestMVC

{

    public class TestClass

    {

        public virtual Boolean Function()

        {

            throw new Exception();

        }

    }

    [TestClass]

    public class MVCUnitTest

    {

        [TestMethod]

        public void MockAlways()

        {

            var mock = new Mock<TestClass>();

           

            //First Return True then Throws exception

            mock.SetupSequence(x => x.Function())

                .Returns(true)

                .Throws(new Exception());

            Assert.AreEqual(mock.Object.Function(), true);

            Assert.AreEqual(mock.Object.Function(), true);

        }

    }

}

We are seeing that it is throwing exception in second call.

CallBase() to call original implementation

This setup is helpful when we want to call the original function rather than mocked function. In this example,Function() is not mocked, we are calling the original function with the help of CallBase(). As we throw an exception from Function() intentionally, the test should throw an exception.

namespace TestMVC

{

    public class TestClass

    {

        public virtual Boolean Function()

        {

            throw new Exception();

        }

    }

    [TestClass]

    public class MVCUnitTest

    {

        [TestMethod]

        public void MockAlways()

        {

            var mock = new Mock<TestClass>();

            mock.CallBase = true;

            mock.SetupSequence(x => x.Function()).CallBase();

               

            Assert.AreEqual(mock.Object.Function(), true);

        }

    }

}

And it’s throwing exception from Function().

Mock Generic class

The mocking mechanism of the generic class is just like normal class mocking. Have a look in the below example:

public class Hello

   {

   }

   public class TestClass <T> where T : class

   {

       public virtual Boolean Function()

       {

           throw new Exception();

       }

   }

   [TestClass]

   public class MVCUnitTest

   {

       [TestMethod]

       public void MockAlways()

       {

           var mock = new Mock<TestClass<Hello>>();

           mock.SetupSequence(x => x.Function()).Returns(true);

           Assert.AreEqual(mock.Object.Function(), true);

       }

   }

Border line

In this article we have learned a few important mock setups using the Moq framework. In my next article I am planning to explore mocking more in depth.