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TDD Workshop

Testing driven development

TDD Diagram

  • Choose a feature to implement.
  • Write a test case.
  • Test should fails. If it passes, the feature is already implemented.
  • Write the implementation. Follow KISS (Keep it simple, stupid).
  • Run your tests to check if it passes.
  • Refactor code to simplify, improve, whatever...

Why testing?

  • Helps prevent future regressions and bugs.
  • Increases confidence that the code works as expected.

Why TDD?

  • Design before implementation 🤔💡.


  • Takes longer to develop (but it can save time in the long run).
  • Testing edge cases is hard.
  • Mocking, faking, and stubbing are all even harder.

But BDD...

Behauvior Driven Development

TDD but tests should describe business logic in business "words".

Kata ⛩

Code kata is an exercise in programming which helps programmers hone their skills through practice and repetition.

For this session, we will follow two exercises:

  • The FizzBuzz kata as general Javascript TDD.
  • A shop list application as visual components TDD.


Only Javascript (ES6+) is required to participate on the session but a very basic knowledge of React is recommended in order to follow the second kata where we build a very simple React app as example of TDD-ing visual components.

Preparing... 🛠

We are going to use Visual Studio Code and Live Share functionality so please, be sure you have installed and configured (logged) this extension. The link session will be distributed on the kata session.

In addition, I recommend you the Jest extension for VS Code but it's not strictly necessary.

Finally, this workshop will use create-react-app as base project so please, ensure you have an empty generated project:

npx create-react-app tdd-workshop

If you check your dependencies, you should have something similar to:

    "@testing-library/jest-dom": "^4.2.4",
    "@testing-library/react": "^9.3.2",
    "@testing-library/user-event": "^7.1.2",
    "react": "^16.13.1",
    "react-dom": "^16.13.1",
    "react-scripts": "3.4.1"

Now, we are ready to rock... 🚀

FizzBuzz kata description

  • Write a program that prints one line for each number from 1 to 100.
  • For multiples of three print Fizz instead of the number.
  • For the multiples of five print Buzz instead of the number.
  • For numbers which are multiples of both three and five print FizzBuzz instead of the number.

Shop list (kata)

  • Should be a list of items.
  • Each item should have a remove link.
  • When the user clicks on remove link, this element should be removed.
  • Should be an input box with an "add button".
  • Button should be disabled when text is empty.
  • Button should be enabled when input has text.
  • When the user clicks on the button, the item should be added to the list.

Interesting links and references

🎧 This workshop has been prepared listening re:member - Ólafur Arnalds

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