csharp-mstest

MSTest Best Practices (MSTest 3.x/4.x)

Your goal is to help me write effective unit tests with modern MSTest, using current APIs and best practices.

Project Setup

Use a separate test project with naming convention [ProjectName].Tests
Reference MSTest 3.x+ NuGet packages (includes analyzers)
Consider using MSTest.Sdk for simplified project setup
Run tests with dotnet test

Test Class Structure

Use [TestClass] attribute for test classes
Seal test classes by default for performance and design clarity
Use [TestMethod] for test methods (prefer over [DataTestMethod])
Follow Arrange-Act-Assert (AAA) pattern
Name tests using pattern MethodName_Scenario_ExpectedBehavior

[TestClass]
public sealed class CalculatorTests
{
    [TestMethod]
    public void Add_TwoPositiveNumbers_ReturnsSum()
    {
        // Arrange
        var calculator = new

Test Lifecycle

Prefer constructors over [TestInitialize] - enables readonly fields and follows standard C# patterns
Use [TestCleanup] for cleanup that must run even if test fails
Combine constructor with async [TestInitialize] when async setup is needed

Execution Order

Assembly Initialization - [AssemblyInitialize] (once per test assembly)
Class Initialization - [ClassInitialize] (once per test class)
Test Initialization (for every test method):
1. Constructor
2. Set TestContext property
3. [TestInitialize]
Test Execution - test method runs
Test Cleanup (for every test method):
1. [TestCleanup]
2. DisposeAsync (if implemented)
3. Dispose (if implemented)
Class Cleanup - [ClassCleanup] (once per test class)
Assembly Cleanup - [AssemblyCleanup] (once per test assembly)

Modern Assertion APIs

MSTest provides three assertion classes: Assert, StringAssert, and CollectionAssert.

Assert Class - Core Assertions

Exception Testing (Prefer over `[ExpectedException]`)

Collection Assertions (Assert class)

String Assertions (Assert class)

Comparison Assertions

Type Assertions

Assert.That (MSTest 4.0+)

StringAssert Class

Note: Prefer Assert class equivalents when available (e.g., Assert.Contains("expected", actual) over StringAssert.Contains(actual, "expected")).

CollectionAssert Class

Note: Prefer Assert class equivalents when available (e.g., Assert.Contains).

Data-Driven Tests

DataRow

DynamicData

The data source can return any of the following types:

IEnumerable<(T1, T2, ...)> (ValueTuple) - preferred, provides type safety (MSTest 3.7+)
IEnumerable<Tuple<T1, T2, ...>> - provides type safety
IEnumerable<TestDataRow> - provides type safety plus control over test metadata (display name, categories)
IEnumerable<object[]> - least preferred, no type safety

Note: When creating new test data methods, prefer ValueTuple or TestDataRow over IEnumerable<object[]>. The object[] approach provides no compile-time type checking and can lead to runtime errors from type mismatches.

TestContext

The TestContext class provides test run information, cancellation support, and output methods. See TestContext documentation for complete reference.

Accessing TestContext

Cancellation Token

Always use TestContext.CancellationToken for cooperative cancellation with [Timeout]:

Test Run Properties

Output and Result Files

Advanced Features

Retry for Flaky Tests (MSTest 3.9+)

Conditional Execution (MSTest 3.10+)

Skip or run tests based on OS or CI environment:

Parallelization

Work Item Traceability (MSTest 3.8+)

Link tests to work items for traceability in test reports:

Work item associations appear in test results and can be used for:

Tracing test coverage to requirements
Linking bug fixes to regression tests
Generating traceability reports in CI/CD pipelines

Common Mistakes to Avoid

Test Organization

Group tests by feature or component
Use [TestCategory("Category")] for filtering
Use [TestProperty("Name", "Value")] for custom metadata (e.g., [TestProperty("Bug", "12345")])
Use [Priority(1)] for critical tests
Enable relevant MSTest analyzers (MSTEST0020 for constructor preference)

Mocking and Isolation

Use Moq or NSubstitute for mocking dependencies
Use interfaces to facilitate mocking
Mock dependencies to isolate units under test

MSTest Best Practices (MSTest 3.x/4.x)

Your goal is to help me write effective unit tests with modern MSTest, using current APIs and best practices.

Project Setup

Use a separate test project with naming convention [ProjectName].Tests
Reference MSTest 3.x+ NuGet packages (includes analyzers)
Consider using MSTest.Sdk for simplified project setup
Run tests with dotnet test

Test Class Structure

Use [TestClass] attribute for test classes
Seal test classes by default for performance and design clarity
Use [TestMethod] for test methods (prefer over [DataTestMethod])
Follow Arrange-Act-Assert (AAA) pattern
Name tests using pattern MethodName_Scenario_ExpectedBehavior

[TestClass]
public sealed class CalculatorTests
{
    [TestMethod]
    public void Add_TwoPositiveNumbers_ReturnsSum()
    {
        // Arrange
        var calculator = new

Test Lifecycle

Prefer constructors over [TestInitialize] - enables readonly fields and follows standard C# patterns
Use [TestCleanup] for cleanup that must run even if test fails
Combine constructor with async [TestInitialize] when async setup is needed

Execution Order

Assembly Initialization - [AssemblyInitialize] (once per test assembly)
Class Initialization - [ClassInitialize] (once per test class)
Test Initialization (for every test method):
1. Constructor
2. Set TestContext property
3. [TestInitialize]
Test Execution - test method runs
Test Cleanup (for every test method):
1. [TestCleanup]
2. DisposeAsync (if implemented)
3. Dispose (if implemented)
Class Cleanup - [ClassCleanup] (once per test class)
Assembly Cleanup - [AssemblyCleanup] (once per test assembly)

Modern Assertion APIs

MSTest provides three assertion classes: Assert, StringAssert, and CollectionAssert.

Assert Class - Core Assertions

Exception Testing (Prefer over `[ExpectedException]`)

Collection Assertions (Assert class)

String Assertions (Assert class)

Comparison Assertions

Type Assertions

Assert.That (MSTest 4.0+)

StringAssert Class

Note: Prefer Assert class equivalents when available (e.g., Assert.Contains("expected", actual) over StringAssert.Contains(actual, "expected")).

CollectionAssert Class

Note: Prefer Assert class equivalents when available (e.g., Assert.Contains).

Data-Driven Tests

DataRow

DynamicData

The data source can return any of the following types:

IEnumerable<(T1, T2, ...)> (ValueTuple) - preferred, provides type safety (MSTest 3.7+)
IEnumerable<Tuple<T1, T2, ...>> - provides type safety
IEnumerable<TestDataRow> - provides type safety plus control over test metadata (display name, categories)
IEnumerable<object[]> - least preferred, no type safety

Note: When creating new test data methods, prefer ValueTuple or TestDataRow over IEnumerable<object[]>. The object[] approach provides no compile-time type checking and can lead to runtime errors from type mismatches.

TestContext

The TestContext class provides test run information, cancellation support, and output methods. See TestContext documentation for complete reference.

Accessing TestContext

Cancellation Token

Always use TestContext.CancellationToken for cooperative cancellation with [Timeout]:

Test Run Properties

Output and Result Files

Advanced Features

Retry for Flaky Tests (MSTest 3.9+)

Conditional Execution (MSTest 3.10+)

Skip or run tests based on OS or CI environment:

Parallelization

Work Item Traceability (MSTest 3.8+)

Link tests to work items for traceability in test reports:

Work item associations appear in test results and can be used for:

Tracing test coverage to requirements
Linking bug fixes to regression tests
Generating traceability reports in CI/CD pipelines

Common Mistakes to Avoid

Test Organization

Group tests by feature or component
Use [TestCategory("Category")] for filtering
Use [TestProperty("Name", "Value")] for custom metadata (e.g., [TestProperty("Bug", "12345")])
Use [Priority(1)] for critical tests
Enable relevant MSTest analyzers (MSTEST0020 for constructor preference)

Mocking and Isolation

Use Moq or NSubstitute for mocking dependencies
Use interfaces to facilitate mocking
Mock dependencies to isolate units under test

MSTest Best Practices (MSTest 3.x/4.x)

Project Setup

Test Class Structure

Test Lifecycle

Execution Order

Modern Assertion APIs

Assert Class - Core Assertions

Exception Testing (Prefer over [ExpectedException])

Collection Assertions (Assert class)

String Assertions (Assert class)

Comparison Assertions

Type Assertions

Assert.That (MSTest 4.0+)

StringAssert Class

CollectionAssert Class

Data-Driven Tests

DataRow

DynamicData

TestContext

Accessing TestContext

Cancellation Token

Test Run Properties

Output and Result Files

Advanced Features

Retry for Flaky Tests (MSTest 3.9+)

Conditional Execution (MSTest 3.10+)

Parallelization

Work Item Traceability (MSTest 3.8+)

Common Mistakes to Avoid

Test Organization

Mocking and Isolation

MSTest Best Practices (MSTest 3.x/4.x)

Project Setup

Test Class Structure

Test Lifecycle

Execution Order

Modern Assertion APIs

Assert Class - Core Assertions

Exception Testing (Prefer over [ExpectedException])

Collection Assertions (Assert class)

String Assertions (Assert class)

Comparison Assertions

Type Assertions

Assert.That (MSTest 4.0+)

StringAssert Class

CollectionAssert Class

Data-Driven Tests

DataRow

DynamicData

TestContext

Accessing TestContext

Cancellation Token

Test Run Properties

Output and Result Files

Advanced Features

Retry for Flaky Tests (MSTest 3.9+)

Conditional Execution (MSTest 3.10+)

Parallelization

Work Item Traceability (MSTest 3.8+)

Common Mistakes to Avoid

Test Organization

Mocking and Isolation

Exception Testing (Prefer over `[ExpectedException]`)

Exception Testing (Prefer over `[ExpectedException]`)