dotnet-test-frameworks

.NET Test Framework Reference

Language-specific detection patterns for .NET test frameworks (MSTest, xUnit, NUnit, TUnit).

Test File Identification

Framework	Test class markers	Test method markers
MSTest	[TestClass]	[TestMethod], [DataTestMethod]
xUnit	(none — convention-based)	[Fact], [Theory]
NUnit	[TestFixture]	[Test], [TestCase], [TestCaseSource]
TUnit	(none — convention-based)	[Test]

Assertion APIs by Framework

Category	MSTest	xUnit	NUnit	TUnit
Equality	Assert.AreEqual	Assert.Equal	Assert.That(x, Is.EqualTo(y))	await Assert.That(x).IsEqualTo(y)
Boolean	Assert.IsTrue / Assert.IsFalse	Assert.True / Assert.False	Assert.That(x, Is.True)	await Assert.That(x).IsTrue() / await Assert.That(x).IsFalse()
Null	Assert.IsNull / Assert.IsNotNull	Assert.Null / Assert.NotNull	Assert.That(x, Is.Null)	await Assert.That(x).IsNull() / await Assert.That(x).IsNotNull()
Exception	Assert.Throws<T>() / Assert.ThrowsExactly<T>()	Assert.Throws<T>()	Assert.That(() => ..., Throws.TypeOf<T>())	await Assert.That(() => ...).Throws<T>() / await Assert.That(() => ...).ThrowsExactly<T>()
Collection	CollectionAssert.Contains	Assert.Contains	Assert.That(col, Has.Member(x))	await Assert.That(col).Contains(x)
String	StringAssert.Contains	Assert.Contains(str, sub)	Assert.That(str, Does.Contain(sub))	await Assert.That(str).Contains(sub)
Type	Assert.IsInstanceOfType	Assert.IsAssignableFrom	Assert.That(x, Is.InstanceOf<T>())	await Assert.That(x).IsAssignableTo<T>() (use await Assert.That(x).IsTypeOf<T>() for exact-type check)
Inconclusive	Assert.Inconclusive()	skip via [Fact(Skip)]	Assert.Inconclusive()	Skip.Test("reason") (no true inconclusive state)
Fail	Assert.Fail()	Assert.Fail() (.NET 10+)	Assert.Fail()	Assert.Fail()

TUnit-specific: assertions are async and must be awaited — a forgotten await causes the assertion to never run, and the test passes silently. A built-in analyzer warns when await is missing. Multiple assertions can be combined with .And / .Or chaining or grouped via Assert.Multiple().

Third-party assertion libraries: Should* (Shouldly), .Should() (FluentAssertions / AwesomeAssertions), Verify() (Verify). TUnit also ships an optional TUnit.Assertions.Should package providing FluentAssertions-style value.Should().BeEqualTo(...) on top of the same infrastructure.

Sleep/Delay Patterns

Pattern	Example
Thread sleep	Thread.Sleep(2000)
Task delay	await Task.Delay(1000)
SpinWait	SpinWait.SpinUntil(() => condition, timeout)

Skip/Ignore Annotations

Framework	Annotation	With reason
MSTest	[Ignore]	[Ignore("reason")]
xUnit	[Fact(Skip = "reason")]	(reason is required)
NUnit	[Ignore("reason")]	(reason is required)
TUnit	[Skip("reason")]	(reason is required; also valid at class and assembly scope, e.g. [assembly: Skip("…")]. Dynamic in-test skipping via Skip.Test("reason").)
Conditional	#if false / #if NEVER	(no reason possible)

Exception Handling — Idiomatic Alternatives

When a test uses try/catch to verify exceptions, suggest the framework-native alternative:

MSTest:

// Instead of try/catch (matches exact type):
var ex = Assert.ThrowsExactly<InvalidOperationException>(
    () => processor.ProcessOrder(emptyOrder));
Assert.AreEqual("Order must contain at least one item", ex.Message);

// Or (also matches derived types):
var ex = Assert.Throws<InvalidOperationException>(
    () => processor.ProcessOrder(emptyOrder));
Assert.AreEqual("Order must contain at least one item", ex.Message);

xUnit:

var ex = Assert.Throws<InvalidOperationException>(
    () => processor.ProcessOrder(emptyOrder));
Assert.Equal("Order must contain at least one item", ex.Message);

NUnit:

var ex = Assert.Throws<InvalidOperationException>(
    () => processor.ProcessOrder(emptyOrder));
Assert.That(ex.Message, Is.EqualTo("Order must contain at least one item"));

TUnit:

await Assert.That(() => processor.ProcessOrder(emptyOrder))
    .Throws<InvalidOperationException>()
    .WithMessage("Order must contain at least one item");

// Or, for exact-type matching (no derived types):
await Assert.That(() => processor.ProcessOrder(emptyOrder))
    .ThrowsExactly<InvalidOperationException>();

Mystery Guest — Common .NET Patterns

Smell indicator	What to look for
File system	File.ReadAllText, File.Exists, File.WriteAllBytes, Directory.GetFiles, Path.Combine with hard-coded paths
Database	SqlConnection, DbContext (without in-memory provider), SqlCommand
Network	HttpClient without HttpMessageHandler override, WebRequest, TcpClient
Environment	Environment.GetEnvironmentVariable, Environment.CurrentDirectory
Acceptable	MemoryStream, StringReader, InMemory database providers, custom DelegatingHandler

Integration Test Markers

Recognize these as integration tests (adjust smell severity accordingly):

• Class name contains Integration, E2E, EndToEnd, or Acceptance
• [TestCategory("Integration")] (MSTest)
• [Trait("Category", "Integration")] (xUnit)
• [Category("Integration")] (NUnit, TUnit)
• Project name ending in .IntegrationTests or .E2ETests

Setup/Teardown Methods

Framework	Setup	Teardown
MSTest	[TestInitialize] or constructor	[TestCleanup] or IDisposable.Dispose / IAsyncDisposable.DisposeAsync
xUnit	constructor	IDisposable.Dispose / IAsyncDisposable.DisposeAsync
NUnit	[SetUp]	[TearDown]
TUnit	[Before(Test)] or constructor	[After(Test)] or IDisposable.Dispose / IAsyncDisposable.DisposeAsync
MSTest (class)	[ClassInitialize]	[ClassCleanup]
NUnit (class)	[OneTimeSetUp]	[OneTimeTearDown]
xUnit (class)	IClassFixture<T>	fixture's Dispose
TUnit (class)	[Before(Class)]	[After(Class)]
TUnit (assembly)	[Before(Assembly)]	[After(Assembly)]
TUnit (session)	[Before(TestSession)]	[After(TestSession)]

TUnit-specific: [BeforeEvery(Test)] / [AfterEvery(Test)] (and the Class / Assembly variants) run for every test/class/assembly across the whole test run — useful for global cross-cutting hooks. Hooks may optionally accept a context object (TestContext, ClassHookContext, etc.) and/or a CancellationToken.