using NUnit.Framework;
 
[TestFixture]
public class CalculatorTests
{
    private Calculator _calculator;
 
    [SetUp]
    public void SetUp() => _calculator = new Calculator();
 
    [Test]
    public void Add_TwoPositiveNumbers_ReturnsSum()
    {
        Assert.That(_calculator.Add(2, 3), Is.EqualTo(5));
    }
 
    [Test]
    public void Divide_ByZero_ThrowsException()
    {
        Assert.Throws<DivideByZeroException>(() => _calculator.Divide(10, 0));
    }
 
    [TearDown]
    public void TearDown() { /* cleanup */ }
}

Assert.That(actual, Is.EqualTo(expected));
Assert.That(actual, Is.Not.EqualTo(unexpected));
Assert.That(value, Is.GreaterThan(5));
Assert.That(value, Is.InRange(1, 10));
Assert.That(str, Does.Contain("hello"));
Assert.That(str, Does.StartWith("He").IgnoreCase);
Assert.That(collection, Has.Count.EqualTo(3));
Assert.That(collection, Has.Member("item"));
Assert.That(collection, Is.All.GreaterThan(0));
Assert.That(obj, Is.Null);
Assert.That(obj, Is.Not.Null);
Assert.That(obj, Is.InstanceOf<MyClass>());
Assert.That(actual, Is.EqualTo(3.14).Within(0.01));
Assert.That(() => Method(), Throws.TypeOf<ArgumentException>()
    .With.Message.Contains("invalid"));

[TestCase(2, 3, 5)]
[TestCase(-1, 1, 0)]
[TestCase(0, 0, 0)]
public void Add_ReturnsCorrectSum(int a, int b, int expected)
{
    Assert.That(_calculator.Add(a, b), Is.EqualTo(expected));
}
 
[TestCaseSource(nameof(DivisionCases))]
public void Divide_ReturnsCorrectQuotient(int a, int b, double expected)
{
    Assert.That(_calculator.Divide(a, b), Is.EqualTo(expected).Within(0.01));
}
 
private static IEnumerable<TestCaseData> DivisionCases()
{
    yield return new TestCaseData(10, 2, 5.0).SetName("10/2=5");
    yield return new TestCaseData(7, 3, 2.33).SetName("7/3=2.33");
}

using Moq;
 
[TestFixture]
public class UserServiceTests
{
    private Mock<IUserRepository> _mockRepo;
    private Mock<IEmailService> _mockEmail;
    private UserService _service;
 
    [SetUp]
    public void SetUp()
    {
        _mockRepo = new Mock<IUserRepository>();
        _mockEmail = new Mock<IEmailService>();
        _service = new UserService(_mockRepo.Object, _mockEmail.Object);
    }
 
    [Test]
    public void CreateUser_SavesAndSendsEmail()
    {
        _mockRepo.Setup(r => r.Save(It.IsAny<User>())).Returns(new User { Id = 1 });
 
        var result = _service.CreateUser("alice@test.com", "Alice");
 
        Assert.That(result.Id, Is.EqualTo(1));
        _mockRepo.Verify(r => r.Save(It.IsAny<User>()), Times.Once);
        _mockEmail.Verify(e => e.SendWelcome("alice@test.com"), Times.Once);
    }
}

[OneTimeSetUp]    → Before all tests in fixture
[SetUp]           → Before each test
[Test]            → Test method
[TearDown]        → After each test
[OneTimeTearDown] → After all tests in fixture

[Test, Category("Smoke")]
public void QuickTest() { }
 
[Test, Ignore("Bug #123")]
public void SkippedTest() { }
 
[Test, Timeout(5000)]
public void TimeLimitedTest() { }
 
[Test, Retry(3)]
public void FlakyTest() { }