csharp-xunit

XUnit Best Practices

Optimized for current .NET SDK releases, C# 12+, xUnit 2.x, and FluentAssertions 6+.

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

• Leverage native parallel subagent dispatch and 200k+ context windows where available.

Anti-Patterns

• Treating fixtures as hidden setup: Readers lose sight of the behavior under test when too much state is shared implicitly.
• Asserting only the happy path: Unit tests miss the contract if failure and edge cases are not explicit.
• Using vague test names: A failing test should explain the broken behavior before anyone opens the body.

Verification Protocol

Before claiming "skill applied successfully":

1. Pass/fail: The Csharp Xunit implementation names the target runtime, framework version, and affected files.
2. Pass/fail: Build, lint, test, or equivalent local validation is run for the changed surface.
3. Pass/fail: Edge cases for errors, dependency drift, and environment differences are addressed or explicitly out of scope.
4. Pressure-test scenario: Apply the workflow to a change that passes happy-path tests but fails one boundary condition.
5. Success metric: Zero untested success claims; every implementation claim maps to a command or artifact.

Before and After Example

// Before
[Fact]
public async Task SavesOrder()
{
    var id = await service.SaveAsync(order);
    Assert.True(id > 0);
}

// After
[Fact]
public async Task SaveAsync_WhenOrderIsValid_PersistsAndReturnsId()
{
    // Arrange
    var order = new Order("ORD-42", 3);

    // Act
    var id = await service.SaveAsync(order);

    // Assert
    id.Should().BeGreaterThan(0);
}

Moves from a vague assertion to an explicit Arrange-Act-Assert flow with a descriptive name.

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