/csharp-xunit

name: csharp-xunit
description: 'Get best practices for XUnit unit testing, including data-driven tests'

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