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C# MSTest

last modified April 12, 2022

C# MSTest tutorial shows how to do unit testing in C# with MSTest framework.

Unit testing is a software testing where individual units (components) of a software are tested. The purpose of unit testing is to validate that each unit of the software performs as designed. A unit is the smallest testable part of any software.

MSTest is a unit-testing library from Microsoft. It is available for all .NET languages. There are other unit-testing libraries including XUnit and NUnit.

We can either place tests in the same project directory or inside a different directory. We start with a simpler option and place tests in the same project directory. In the end, we place tests in a different directory within a solution.

$ dotnet add package Microsoft.NET.Test.Sdk
$ dotnet add package MSTest.TestAdapter
$ dotnet add package MSTest.TestFramework

In order to use MSTest, we need to add these three libraries.

C# MSTest simple example

We start with a simple example.

Arith.cs
namespace Messages.Services;

public class Messages
{
    public static Func<string> msg1 = () => "Hello there!";
    public static Func<string> msg2 = () => "Good Morning!";
}

We test simple message functions.

We put our tests into the tests directory. MSTest automatically discovers our tests.

tests/MessageTest.cs
namespace Messages.Tests;

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Messages.Services;

[TestClass]
public class MessageTest
{
    private const string Expected1 = "Hello there!";
    private const string Expected2 = "Good Morning!";

    [TestMethod]
    public void Message1()
    {
        var m1 = Messages.msg1();

        Assert.AreEqual(Expected1, m1);
    }

    [TestMethod]
    public void Message2()
    {
        var m2 = Messages.msg2();

        Assert.AreEqual(Expected2, m2);
    }
}

The class is annotated with the [TestClass] attribute, the test methods are annotated with the [TestMethod] attribute. We use assertions to ensure the correct output.

$ dotnet test 
... 
Starting test execution, please wait...
A total of 1 test files matched the specified pattern.

Passed!  - Failed:     0, Passed:     2, Skipped:     0, Total:     2, ...

C# MSTest parameterized tests

The [DataTestMethod] attribute indicates a parameterized method. The parameters are added with the [DataRow] attribute.

Arith.cs
namespace Arithmetic.Services;

public class Basic
{
    public static Func<int, int, int> add = (a, b) => a + b;
    public static Func<int, int, int> mul = (a, b) => a * b;
    public static Func<int, int, int> sub = (a, b) => a - b;
    public static Func<int, int, int> div = (a, b) => a / b;
}

We are going to test simple arithmetic functions.

tests/ArithTest.cs
namespace Messages.Tests;

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Arithmetic.Services;

[TestClass]
public class ArithTest
{
    [DataTestMethod]
    [DataRow(1, 2, 3)]
    [DataRow(2, 2, 4)]
    [DataRow(-1, 4, 3)]
    public void Add(int x, int y, int expected)
    {
        int r = Basic.add(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DataRow(1, 2, -1)]
    [DataRow(2, 2, 0)]
    [DataRow(3, 2, 1)]
    public void Sub(int x, int y, int expected)
    {
        int r = Basic.sub(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DataRow(9, 3, 27)]
    [DataRow(3, 3, 9)]
    [DataRow(-3, -3, 9)]
    public void Mul(int x, int y, int expected)
    {
        int r = Basic.mul(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DataRow(9, 3, 3)]
    [DataRow(3, 3, 1)]
    [DataRow(8, 2, 4)]
    public void Div(int x, int y, int expected)
    {
        int r = Basic.div(x, y);
        Assert.AreEqual(r, expected);
    }
}

In this example, we test each method with three sets of values.

[DataTestMethod]
[DataRow(1, 2, 3)]
[DataRow(2, 2, 4)]
[DataRow(-1, 4, 3)]
public void Add(int x, int y, int expected)
{
    int r = Basic.add(x, y);
    Assert.AreEqual(r, expected);
}

We are testing the Add method. The method is tested with three sets of values given by the [DataRow] attribute. The calculated and expected values are compared with Assert.AreEqual assertion.

C# MSTest skipping tests

Test methods can be skipped with [Ignore] attribute.

tests/ArithTest.cs
namespace Arithmetic.Tests;

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Arithmetic.Services;

[TestClass]
public class ArithTest
{
    [DataRow(1, 2, 3)]
    [DataRow(2, 2, 4)]
    [DataRow(-1, 4, 3)]
    [DataTestMethod]
    public void Add(int x, int y, int z)
    {
        int r = Basic.add(x, y);
        Assert.AreEqual(r, z);
    }

    [DataTestMethod]
    [DataRow(1, 2, -1)]
    [DataRow(2, 2, 0)]
    [DataRow(3, 2, 1)]
    public void Sub(int x, int y, int z)
    {
        int r = Basic.sub(x, y);
        Assert.AreEqual(r, z);
    }

    [DataTestMethod]
    [DataRow(9, 3, 27)]
    [DataRow(3, 3, 9)]
    [DataRow(-3, -3, 9)]
    [Ignore]
    public void Mul(int x, int y, int z)
    {
        int r = Basic.mul(x, y);
        Assert.AreEqual(r, z);
    }

    [DataTestMethod]
    [DataRow(9, 3, 3)]
    [DataRow(3, 3, 1)]
    [DataRow(8, 2, 4)]
    [Ignore]
    public void Div(int x, int y, int z)
    {
        int r = Basic.div(x, y);
        Assert.AreEqual(r, z);
    }
}

We have four test methods. Two of them are skipped using the [Ignore] attribute.

$ dotnet test
...
Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
  Skipped Mul (9,3,27)
  Skipped Mul (3,3,9)
  Skipped Mul (-3,-3,9)
  Skipped Div (9,3,3)
  Skipped Div (3,3,1)
  Skipped Div (8,2,4)

Passed!  - Failed:     0, Passed:     6, Skipped:     6, Total:    12, Duration: 84 ms ...

C# MSTest DynamicData

With [DynamicData] attribute, we can externalize the test data into a method or a property.

tests/ArithTest.cs
namespace Messages.Tests;

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Arithmetic.Services;

[TestClass]
public class Tests
{
    [DataTestMethod]
    [DynamicData(nameof(AddData), DynamicDataSourceType.Method)]
    public void Add(int x, int y, int expected)
    {
        int r = Basic.add(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DynamicData(nameof(SubData), DynamicDataSourceType.Method)]
    public void Sub(int x, int y, int expected)
    {
        int r = Basic.sub(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DynamicData(nameof(MulData), DynamicDataSourceType.Method)]
    public void Mul(int x, int y, int expected)
    {
        int r = Basic.mul(x, y);
        Assert.AreEqual(r, expected);
    }

    [DataTestMethod]
    [DynamicData(nameof(DivData), DynamicDataSourceType.Method)]
    public void Div(int x, int y, int expected)
    {
        int r = Basic.div(x, y);
        Assert.AreEqual(r, expected);
    }

    private static IEnumerable<object[]> AddData()
    {
        return new[]
        {
            new object[] { 1, 2, 3 },
            new object[] { 2, 2, 4 },
            new object[] { -1, 4, 3 }
        };
    }

    private static IEnumerable<object[]> SubData()
    {
        return new[]
        {
            new object[] { 1, 2, -1 },
            new object[] { 2, 2, 0 },
            new object[] { 3, 2, 1 }
        };
    }

    private static IEnumerable<object[]> MulData()
    {
        return new[]
        {
            new object[] { 9, 3, 27 },
            new object[] { 3, 3, 9 },
            new object[] { -3, -3, 9 }
        };
    }

    private static IEnumerable<object[]> DivData()
    {
        return new[]
        {
            new object[] { 9, 3, 3 },
            new object[] { 3, 3, 1 },
            new object[] { 8, 2, 4 }
        };
    }
}

In the example, we have test data in separate methods.

Placing tests in separate directory

In the following example, we show how to place tests in a separate directory.

$ mkdir Separate
$ cd Separate

We create a new directory.

$ dotnet new sln

We create a new empty solution.

$ mkdir PalindromeService PalindromeService.Tests

Two directories are created.

$ cd PalindromeService
$ dotnet new classlib

We create a new library.

PalindromeService\PalindromeService.cs
namespace Palindrome.Services;
  
using System.Globalization;

public class PalindromeService
{
    public bool IsPalindrome(string word)
    {
        IEnumerable<string> GraphemeClusters(string s)
        {
            var enumerator = StringInfo.GetTextElementEnumerator(s);
            while (enumerator.MoveNext())
            {
                yield return (string)enumerator.Current;
            }
        }

        var reversed = string.Join("", GraphemeClusters(word).Reverse().ToArray());

        return reversed == word;
    }
}

The PalindromeService contains the IsPalindrome method, which determines if a words is a palindrome.

$ cd .. 
$ dotnet sln add PalindromeService\PalindromeService.csproj

We add the PalindromeService to the solution.

$ cd PalindromeService.Tests
$ dotnet new mstest
$ dotnet add reference ..\PalindromeService\PalindromeService.csproj

We go to the PalindromeService.Tests directory and add the unit libraries add the reference to the PalindromeService.

PalindromeService.Tests\PalindromeService.Tests.csproj
<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>

    <IsPackable>false</IsPackable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
    <PackageReference Include="MSTest.TestAdapter" Version="2.2.8" />
    <PackageReference Include="MSTest.TestFramework" Version="2.2.8" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\PalindromeService\PalindromeService.csproj" />
  </ItemGroup>
</Project>

This is how the project file looks like.

PalindromeService.Tests\Tests.cs
namespace Palindrome.Services.Tests;

using Microsoft.VisualStudio.TestTools.UnitTesting;

[TestClass]
public class Tests
{
    private PalindromeService? _palindromeService;

    [TestInitialize]
    public void SetUp()
    {
        _palindromeService = new PalindromeService();
    }

    [DataTestMethod]
    [DataRow("racecar")]
    [DataRow("level")]
    [DataRow("nun")]
    public void IsPalindrome(string word)
    {
        var r = _palindromeService!.IsPalindrome(word);
        Assert.AreEqual(r, true);
    }
}

We test the IsPalindrome method with three words.

[TestInitialize]
public void SetUp()
{
    _palindromeService = new PalindromeService();
}

The [TestInitialize] attribute is used to provide a common set of functions that are performed just before each test method is called. In our case, we create the PalindromeService.

$ cd ..
$ dotnet sln add PalindromeService.Tests\PalindromeService.Tests.csproj

We add the test project to the solution.

$ dotnet test

Finally, we can run the tests.

In this tutorial we have done unit testing in C# with MSTest library.

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