XUnit Best Practices

Your goal is to help me write effective unit tests with XUnit, covering both standard and data-driven testing approaches.

Project Setup

• Use a separate test project with naming convention

  [ProjectName].Tests

• Reference Microsoft.NET.Test.Sdk, xunit, and xunit.runner.visualstudio packages
• Create test classes that match the classes being tested (e.g.,

  CalculatorTests

  for

  Calculator

  )
• Use .NET SDK test commands:

  dotnet test

  for running tests

Test Structure

• No test class attributes required (unlike MSTest/NUnit)
• Use fact-based tests with

  [Fact]

  attribute for simple tests
• Follow the Arrange-Act-Assert (AAA) pattern
• Name tests using the pattern

  MethodName_Scenario_ExpectedBehavior

• Use constructor for setup and

  IDisposable.Dispose()

  for teardown
• Use

  IClassFixture<T>

  for shared context between tests in a class
• Use

  ICollectionFixture<T>

  for shared context between multiple test classes

Standard Tests

• Keep tests focused on a single behavior
• Avoid testing multiple behaviors in one test method
• Use clear assertions that express intent
• Include only the assertions needed to verify the test case
• Make tests independent and idempotent (can run in any order)
• Avoid test interdependencies

Data-Driven Tests

• Use

  [Theory]

  combined with data source attributes
• Use

  [InlineData]

  for inline test data
• Use

  [MemberData]

  for method-based test data
• Use

  [ClassData]

  for class-based test data
• Create custom data attributes by implementing

  DataAttribute

• Use meaningful parameter names in data-driven tests

Assertions

• Use

  Assert.Equal

  for value equality
• Use

  Assert.Same

  for reference equality
• Use

  Assert.True

  /

  Assert.False

  for boolean conditions
• Use

  Assert.Contains

  /

  Assert.DoesNotContain

  for collections
• Use

  Assert.Matches

  /

  Assert.DoesNotMatch

  for regex pattern matching
• Use

  Assert.Throws<T>

  or

  await Assert.ThrowsAsync<T>

  to test exceptions
• Use fluent assertions library for more readable assertions

Mocking and Isolation

• Consider using Moq or NSubstitute alongside XUnit
• Mock dependencies to isolate units under test
• Use interfaces to facilitate mocking
• Consider using a DI container for complex test setups

Test Organization

• Group tests by feature or component
• Use

  [Trait("Category", "CategoryName")]

  for categorization
• Use collection fixtures to group tests with shared dependencies
• Consider output helpers (

  ITestOutputHelper

  ) for test diagnostics
• Skip tests conditionally with

  Skip = "reason"

  in fact/theory attributes