Write tests with MSTest

In this article, you learn about the APIs and conventions used by MSTest to help you write and shape your tests.

Note

Attribute names ending with "Attribute" can use the short form. TestClass and TestClassAttribute are equivalent. Attributes with parameterless constructors can omit parentheses.

Test structure

Every MSTest test class must have the TestClass attribute, and every test method must have the TestMethod attribute:

using Microsoft.VisualStudio.TestTools.UnitTesting;

[TestClass]
public class CalculatorTests
{
    [TestMethod]
    public void Add_TwoNumbers_ReturnsSum()
    {
        // Arrange
        var calculator = new Calculator();

        // Act
        var result = calculator.Add(2, 3);

        // Assert
        Assert.AreEqual(5, result);
    }
}

TestClassAttribute

The TestClassAttribute marks a class that contains tests and, optionally, initialize or cleanup methods. You can extend this attribute to customize test class behavior.

TestMethodAttribute

The TestMethodAttribute marks a method as a test to run. Test methods must be:

• Instance methods (not static)
• Public
• Return void, Task, or ValueTask (MSTest v3.3+)
• Parameterless, unless using data-driven attributes

[TestClass]
public class TestMethodExamples
{
    [TestMethod]
    public void SynchronousTest()
    {
        Assert.IsTrue(true);
    }

    [TestMethod]
    public async Task AsynchronousTest()
    {
        await Task.Delay(100);
        Assert.IsTrue(true);
    }
}

Warning

Don't use async void for test methods. Use async Task or async ValueTask instead.

DiscoverInternalsAttribute

The DiscoverInternalsAttribute assembly attribute enables MSTest to discover internal test classes and methods. By default, only public tests are discovered. This attribute is particularly useful when you have parameterized tests that use internal types as parameters:

[assembly: DiscoverInternals]

internal record TestInput(int Value, string Description);

[TestClass]
public class CalculatorTests
{
    internal static IEnumerable<TestInput> TestData
    {
        get
        {
            yield return new TestInput(1, "one");
            yield return new TestInput(2, "two");
        }
    }

    [TestMethod]
    [DynamicData(nameof(TestData))]
    internal void Add_WithTestInput_ReturnsExpected(TestInput input)
    {
        var calculator = new Calculator();
        var result = calculator.Add(input.Value, 1);
        Assert.AreEqual(input.Value + 1, result);
    }
}

Without DiscoverInternals, the test method and its internal TestInput parameter type wouldn't be discovered by the test runner.

Core concepts

MSTest documentation is organized by topic:

Topic	Description
Assertions	Verify expected results with Assert classes
Data-driven testing	Run tests with multiple inputs (DataRow, DynamicData)
Test lifecycle	Setup and cleanup at assembly, class, and test levels
Execution control	Threading, parallelization, timeouts, retries, and conditional execution
Test organization	Categories, priorities, owners, and metadata
TestContext	Access test runtime information

Attribute quick reference

Category	Attributes	See
Test identification	TestClass, TestMethod, DiscoverInternals	This page
Data-driven	DataRow, DynamicData, TestDataRow	Data-driven testing
Lifecycle	AssemblyInitialize, ClassInitialize, TestInitialize, and cleanup counterparts	Test lifecycle
Threading	STATestClass, STATestMethod, UITestMethod	Execution control
Parallelization	Parallelize, DoNotParallelize	Execution control
Timeout/Retry	Timeout, Retry	Execution control
Conditional	Ignore, OSCondition, CICondition	Execution control
Metadata	TestCategory, TestProperty, Owner, Priority	Test organization
Work tracking	WorkItem, GitHubWorkItem	Test organization

Assertions

Use the Assert classes of the Microsoft.VisualStudio.TestTools.UnitTesting namespace to verify specific functionality. A test method exercises code in your application, but it reports correctness only when you include Assert statements.

MSTest assertions are divided into:

• Assert class: General-purpose assertions (AreEqual, IsTrue, ThrowsException)
• StringAssert class: String-specific assertions (Contains, Matches, StartsWith)
• CollectionAssert class: Collection assertions (Contains, AllItemsAreUnique, AreEquivalent)

Testing private members

You can test private members using reflection wrapper classes:

• PrivateObject: For private instance methods
• PrivateType: For private static methods

Tip

Consider whether private methods need direct testing. Often, testing through public interfaces provides better coverage and more maintainable tests.

See also

• Get started with MSTest
• MSTest analyzers
• Unit testing best practices
• Run selective unit tests