Creating an xUnit Test Project
Add a new project: File → New → Project → xUnit Test Project (.NET). Reference your main project. xUnit discovers test methods marked with [Fact] (single test) or [Theory] (parameterised).
First tests
CalculatorTests.cs
using Xunit;
public class Calculator
{
public int Add(int a, int b) => a + b;
public double Divide(double a, double b)
{
if (b == 0) throw new DivideByZeroException();
return a / b;
}
}
public class CalculatorTests
{
private readonly Calculator _calc = new();
[Fact]
public void Add_TwoPositives_ReturnsSum()
{
int result = _calc.Add(3, 4);
Assert.Equal(7, result);
}
[Theory]
[InlineData(10, 2, 5)]
[InlineData(9, 3, 3)]
[InlineData(7, 2, 3.5)]
public void Divide_ValidInputs_ReturnsCorrectQuotient(double a, double b, double expected)
{
Assert.Equal(expected, _calc.Divide(a, b), precision: 5);
}
[Fact]
public void Divide_ByZero_ThrowsException()
{
Assert.Throws(() => _calc.Divide(5, 0));
}
} Running Tests
Open the Test Explorer (Test → Test Explorer). Click Run All or run a single test. Green = pass, Red = fail. The output panel shows assertion failure details.
Mocking with Moq
Install Moq via NuGet to create mock objects for testing classes with dependencies.
Moq example
MockTest.cs
using Moq;
using Xunit;
public interface IEmailSender { void Send(string to, string msg); }
public class OrderService(IEmailSender mailer)
{
public void PlaceOrder(string product)
=> mailer.Send("[email protected]", $"Order placed: {product}");
}
public class OrderServiceTests
{
[Fact]
public void PlaceOrder_SendsEmail()
{
var mock = new Mock();
var svc = new OrderService(mock.Object);
svc.PlaceOrder("Widget");
mock.Verify(m => m.Send(
"[email protected]",
It.Is(s => s.Contains("Widget"))), Times.Once);
}
}