Why and What to Test

Why and What to Test

In this lesson — part of Testing Fundamentals — you'll learn why and what to test in C# and why it matters in real work.

Why it matters

Tests prove your code works and keep it working as you change it.

Key ideas

• What to test
• Arrange-Act-Assert
• Running a test suite
• Good vs. brittle tests

In practice

Here's how it looks in idiomatic C#:

using Xunit;

public class MathTests
{
    [Fact]
    public void Add_ReturnsSum()
    {
        int result = 2 + 3;
        Assert.Equal(5, result);
    }
}

C# note: xUnit marks test methods with [Fact] and uses Assert.Equal(expected, actual) ordering; MSTest and NUnit are the other common frameworks.

Try it yourself

Exercise: In C#, write three tests for a function that reverses a string.

Recap

You now understand why and what to test and can apply it in C#. Mark this lesson complete and continue to the next one.