Javascript TDD with ChatGPT

April 5th, 2023
Test-driven development in Javascript with ChatGPT-4 works. An example demonstrates it using a precise description and refined prompt engineering.
Screen with Javascript code

Previously, I wrote about programming with ChatGPT in an iterative approach followed by TDD with Python. Now that ChatGPT-4 is available, it is time to revisit the TDD (Test Driven Development) approach with Javascript for a change.

The setup is the same. Write the tests for an ASIN check function and then implement it. However, I now use ChatGPT-4, not 3.5 and some refined prompts.

ChatGPT TDD prompting

The strategy is to define the behaviour and constraints, not the tests, first. They are language-independent, and we can generate any language from this in the following steps.

> The function is_asin takes a string and returns a boolean. It returns true if the passed parameter adheres to the definition of an ASIN (Amazon Standard Identification Number). An ASIN is a ten-character long alphanumeric identifier with chars being uppercase. 

  • Create a list of unit tests for a function called is_asin

  • Start the list with a happy path example

  • Do not assume a programming language

  • Do not show any code

  • Use best practices

  • Be concise, i.e. use as few tests as sensible

Most items are self-explanatory. A simple yet important point is asking to use best practices. It commonly increases the code quality, resulting in professional styles, structures and code instead of simple beginner or tutorial solutions. The answer is a list of test cases described in plain English.

Next, we ask for the unit tests.

> Implement the unit tests in Javascript.

The resulting tests are exhaustive and yet simple tying down the behaviour nicely.

> Here's a sample implementation of the unit tests using JavaScript and the Jest testing framework:

const is_asin = require('./is_asin'); // Assuming the function is exported from is_asin.js

describe('is_asin', () => {
  test('Happy path test', () => {

  test('Length test - shorter than 10 characters', () => {

  test('Length test - longer than 10 characters', () => {

  test('Case sensitivity test', () => {

  test('Non-alphanumeric characters test', () => {

  test('Empty string test', () => {

  test('Null input test', () => {

  test('Unicode characters test', () => {

  test('Numeric-only test', () => {

  test('Alpha-only test', () => {

Remember to have Jest installed in your project by running npm install --save-dev jest, and include the is_asin function implementation in a separate file called is_asin.js.

Next, we ask for the code with a reminder to do its best and document it.

> Implement is_asin using best practices including documentation.

ChatGPT provides a decent, documented, working solution. Professional software engineers will be able to improve this further. In fact, ChatGPT can, too, if prompted.

> Here's an implementation of the is_asin function using best practices and including documentation:

 * Checks if the given string is a valid Amazon Standard Identification Number (ASIN).
 * @param {string} input - The string to check for ASIN validity.
 * @returns {boolean} True if the input string is a valid ASIN, false otherwise.
function is_asin(input) {
  // Check if input is a string
  if (typeof input !== 'string') {
    return false;

  // Check if input has the correct length
  if (input.length !== 10) {
    return false;

  // Check if input contains only uppercase alphanumeric characters
  const uppercaseAlphanumericRegex = /^[A-Z0-9]*$/;
  return uppercaseAlphanumericRegex.test(input);

module.exports = is_asin;

This implementation includes a function description, parameter description, and return value description in the form of JSDoc comments. The function also checks for edge cases, such as the input not being a string, having an incorrect length, or not containing only uppercase alphanumeric characters.


It is impressive how ChatGPT is progressing. At the same time, it strongly depends on the user correctly prompting, which currently takes some experience and skill. Compared to the previous example, this Javascript TDD ChatGPT-4 solution worked on the first attempt. But it did use a newer version, and I used improved prompts too.

Christian Prokopp, Founder

    Let's talk

    You have a business problem in need for data and analysis? Send us an email.

    Subscribe to updates

    Join Bold Data's email list to receive free data and updates.

Related Posts

9 Proven Programming Productivity Prompt Tips for ChatGPT

Cyborg red eyes
Learn to harness the potential of ChatGPT4, your virtual programming partner, with nine prompting tips. Improve your programming skills by communicating clearly, engaging in conversation, using the proper syntax, and iterating on complexity. Keep context fresh, and ChatGPT4 will be invaluable in your coding journey.

Deep Dive into Code with ChatGPT

Deep diver
Open Source libraries offer user documentation. But expert users and contributors have a deeper understanding of the inner workings stemming from a mental model and architecture derived from deep dives into the code. That understanding and model are helpful to employ the library more effectively, debug issues when using it, and teach interesting concepts on how to structure complex reusable code.

Understanding the Power of ChatGPT

A robot and a teacher in school
ChatGPT is a state-of-the-art language model developed by OpenAI, utilising the Transformer model and fine-tuned through reinforcement learning to produce accurate and ethical text responses.

How to create a Data Dictionary using ChatGPT

An abstract watercolour art of a robot reading a dictionary
ChatGPT can combine data with natural language and has extensive information about most subjects. That lends itself to novel applications like creating informative data dictionaries.

Python TDD with ChatGPT

Being tested
Programming with ChatGPT using an iterative approach is difficult, as I have demonstrated previously. Maybe ChatGPT can benefit from Test-driven development (TDD). Could it aid LLMs as it does humans?

How to code Python with ChatGPT

Meditating robot
Can ChatGPT help you develop software in Python? Let us ask ChatGPT to write code to query AWS Athena to test if and how we can do it step-by-step.

One simple thing companies miss about their data

When you can't see the wood for the trees
There is one simple thing most companies miss about their data. It has been instrumental in my work as a data professional ever since.

Why I became a Solo Founder

Single lego figure walking in sand
I never wanted to be a solo founder. Yet, in 2021, I quit my job and started Bold Data to mine the Internet single-handedly. Trust me, it sounds as insane to write as to read. What on earth possessed me, and more importantly, would I do it again?

All Blog Posts

See the full list of blog posts to read more.
Subscribe for updates, free datasets and analysis.