How to Use MSTest in C#: Simple Guide with Example

To use MSTest in C#, create a test project, add the Microsoft.VisualStudio.TestTools.UnitTesting namespace, and write test methods marked with [TestMethod] inside a class marked with [TestClass]. Run tests using Visual Studio Test Explorer or the dotnet test command.

Syntax

Use [TestClass] to mark a class that contains tests. Use [TestMethod] to mark each test method. Inside test methods, use Assert methods to check expected results.

• [TestClass]: Identifies the test container class.
• [TestMethod]: Marks a method as a test.
• Assert: Provides methods to verify test outcomes.

csharp

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace MyTests
{
    [TestClass]
    public class CalculatorTests
    {
        [TestMethod]
        public void Add_TwoNumbers_ReturnsSum()
        {
            // Arrange
            int a = 5;
            int b = 3;
            
            // Act
            int result = a + b;

            // Assert
            Assert.AreEqual(8, result);
        }
    }
}

Example

This example shows a simple test class for a calculator's addition method. It demonstrates how to write a test method that checks if adding two numbers returns the correct sum.

csharp

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace CalculatorApp.Tests
{
    [TestClass]
    public class CalculatorTests
    {
        [TestMethod]
        public void Add_TwoPositiveNumbers_ReturnsCorrectSum()
        {
            // Arrange
            var calculator = new Calculator();
            int x = 10;
            int y = 20;

            // Act
            int result = calculator.Add(x, y);

            // Assert
            Assert.AreEqual(30, result);
        }
    }

    public class Calculator
    {
        public int Add(int a, int b)
        {
            return a + b;
        }
    }
}

Output

Test run successful.
Total tests: 1
     Passed: 1
 Total time: 1.2345 Seconds

Common Pitfalls

Common mistakes when using MSTest include:

• Forgetting to mark the test class with [TestClass] or test methods with [TestMethod], so tests are not discovered.
• Not referencing the MSTest NuGet package, causing missing namespace errors.
• Using Assert incorrectly, such as comparing wrong values or forgetting to assert results.
• Running tests without building the project first, leading to stale results.

csharp

/* Wrong: Missing [TestMethod] attribute, test won't run */
[TestClass]
public class SampleTests
{
    public void TestWithoutAttribute()
    {
        Assert.IsTrue(true);
    }
}

/* Correct: Add [TestMethod] attribute */
[TestClass]
public class SampleTests
{
    [TestMethod]
    public void TestWithAttribute()
    {
        Assert.IsTrue(true);
    }
}

Quick Reference

Attribute/Method	Purpose
[TestClass]	Marks a class that contains test methods
[TestMethod]	Marks a method as a test to run
Assert.AreEqual(expected, actual)	Checks if two values are equal
Assert.IsTrue(condition)	Checks if a condition is true
Assert.IsFalse(condition)	Checks if a condition is false
Assert.ThrowsException(action)	Checks if an exception of type T is thrown

Key Takeaways

Mark test classes with [TestClass] and test methods with [TestMethod] to enable MSTest discovery.

Use Assert methods to verify expected outcomes inside test methods.

Add the MSTest NuGet package to your project to access MSTest features.

Run tests via Visual Studio Test Explorer or the dotnet test command.

Avoid missing attributes or incorrect asserts to ensure tests run and validate correctly.