Csharp-Xunit

# 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