What is TDD in simple words 🤔
First you formulate waiting in the form of dough.
The test fails — great, it means it catches the lack of implementation.
You write minimum code to make the test turn green.
Refactoring without fear — tests will not let you "break" the behavior.
Meaning: think about requirements before implementation. This saves time on debugging and rewriting.
Mini code examples 📎
Python (pytest)
# test_math_utils.py
from math_utils import is_even
def test_is_even_basic():
assert is_even(2) is True
assert is_even(3) is False
# math_utils.py (minimum implementation)
def is_even(n: int) -> bool:
return n % 2 == 0JavaScript (Vitest/Jest)
// math.test.js
import { isEven } from "./math.js";
test("isEven basic", () => {
expect(isEven(2)).toBe(true);
expect(isEven(3)).toBe(false);
});
// math.js (minimum implementation)
export const isEven = (n) => n % 2 === 0;Feeling "too simple" is normal. In TDD, this is how it should be: small step → feedback → improvement.
Why a beginner should try 🎯
Beginner's problem | How TDD helps |
|---|---|
Vague task | The test forces you to formulate precise criteria |
Fear of refactoring | Green tests are an insurance that the behavior has been preserved |
Bugs pop up late | Tests catch errors immediately after code changes |
It is difficult to assess progress | With each green test, you can see that it has improved |
How to get started: a step-by-step plan 🧭
Choose a small function (strings, numbers, validations).
Write one test: the most obvious happy-path.
Make it green with minimal code (not perfect — it just works).
Add another test (extreme case/error) — again green.
Refactor names, structure, remove duplicates.
Repeat until the requirements are closed.
Mini-practice (20 minutes): Implement the slugify(title) function (converts the title into a URL slug).
Test 1: "Hello world!" →
privet-mirTest 2: double spaces → one hyphen
Test 3: upper case → lower case
Common mistakes and how to avoid them 🧯
Write a lot of tests at once. Do small iterations, otherwise you will lose focus.
Immediately "perfect" code. First "green", then beauty (refactoring).
Tests depend on the outside world. Isolate: mocks/stubs, pure functions, fixed data.
Complex integration scenarios from scratch. Start with unit tests of the logic core.
Where to integrate TDD in real tasks 🧩
Data formatting (validators, parsers, calculations).
"Business rules" (discounts, accesses, order statuses).
Small utilities in the UI (input masks, sorting, filters).
Even 30–50% coverage of key logic is already a huge increase in confidence.
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Summary 🏁
TDD is about clarity of requirements and calm refactoring. Start with small functions, keep the cycle short and DO NOT chase perfection until it's "green". Then you improve. This way you get to a neat and verifiable code faster.
Which function will you test first — slugify, email validation or discount calculator? 🙂