Unit Testing in .NET: A Comprehensive Guide

Mastering Unit Testing in .NET with xUnit Unit testing is a fundamental practice in modern software development. It focuses on testing the smallest units of code—typically individual methods—to ensure they behave correctly in isolation. In the .NET ecosystem, the most commonly used testing frameworks are: xUnit NUnit MSTest Among these, xUnit is widely preferred due to its simplicity, extensibility, and performance. 1. The AAA Pattern (Arrange, Act, Assert) A well-structured unit test follows the AAA pattern: Arrange: Prepare inputs and dependencies Act: Execute the method Assert: Verify the result Example [ Fact ] public void CalculateTax_ShouldReturnTwentyPercent_WhenIncomeIsHigh () { var calculator = new TaxCalculator (); decimal income = 100000 ; var result = calculator . Calculate ( income ); Assert . Equal ( 20000 , result ); } 2. Fact vs Theory in xUnit Fact Used for fixed input tests. [ Fact ] public void IsAdult_ShouldReturnTrue_WhenAgeIsAbove18 () { var user = new User (); va