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 D 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 the idea in pseudocode — the exact syntax varies by language:

// D: a unit test
test("adds", () => expect(add(2,2)).toBe(4))

Try it yourself

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

Recap

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