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