What tool or library have you used for test automation in your projects?

For test automation in C# projects, the following tools are often used:

• NUnit — a popular framework for unit testing, supports attributes for describing tests, and is easy to integrate with CI.
• xUnit.net — a modern framework focused on simplicity and extensibility.
• MSTest — a testing framework built into Visual Studio.
• Moq — a library for creating mock objects, helps isolate the components under test.

Example of a simple test with NUnit:

using NUnit.Framework;

[TestFixture]
public class CalculatorTests
{
    [Test]
    public void Add_WhenCalled_ReturnsSum()
    {
        var calculator = new Calculator();
        var result = calculator.Add(2, 3);
        Assert.AreEqual(5, result);
    }
}

The choice of a specific tool depends on the project requirements and team preferences, but NUnit and xUnit are the most common.