CCTDD: Cypress Component Test Driven Design

Foreword

I believe applying TDD with Cypress Component Testing can take our front end engineering to the next level.
In this book we will recreate Angular's Tour of Heroes, in a component test driven manner, using Cypress, React and TS. Once we build up the components, we will investigate how TDD can be practiced with routing, state management and Cypress e2e testing. We will also learn about API e2e testing with Cypress, and see where UI-integration tests fit.
For the requirement spec, we will use the Angular version of the app. In the first half the book, we will use Cypress component testing with a test driven design approach to engineer our components. We will work on the child components first and work our way up. We will use console.log for the click event handlers until we have to make decisions about them.
In the later chapters when we tackle state and routing, Cypress e2e testing will become more relevant for TDD, and the component test suite will serve as the reassurance that our app still works as expected.
In every chapter we will explicitly capture Red Green Refactor cycles of TDD, and will wrap with a 1:1 comparison of the Cypress component test to React Testing Library, followed by a summary & key takeaways. Every code sample is meant to be copy pastable and to give reproducible results, however the reader is encouraged to write and incrementally improve the code rather than copy paste. One final disclaimer; in the early chapters, to avoid major rehash of files and code later, we might make some decisions towards being more aligned with the final version of the app.
Years ago John Papa created the same app in Angular, Vue and ReactJS, alas the React version is dated, and as the React community we know how frequently the meta changes. The approach gives readers coming from Vue and Angular the opportunity to make 1:1 comparisons when writing Cypress component tests, and even a possibility to redo this exercise in one of those frameworks.

Acknowledgements

Many thanks to the reviewers of this content; Matthew Schrepel, Stefano Magni, Gleb Bahmutov and to Kent C. Dodds for continuously answering questions during his Epic React office hours.
These are the resources that have inspired the content of this book.

GitHub repos with Cypress Component + e2e examples

Future

Making comparisons and contrasts are a great way to learn new tech. There aren't too many resources that are fashioned in this style. For example in this content Heroes are using React props to pass state between components, and their mirror Villains are using the React context api.
This is a live book keeping updated and improved daily. We can have a Redux mirror, a Redux Toolkit mirror, an X-State mirror, perhaps one day we can migrate the application to NextJs. Expect to see more chapters in the future and learn more about front-end development together.

Questions, Comments & Feedback

For all the above you can start a discussion or open an issue at the CCTDD GitHub repo.

Setup

Use this template to create a new repository. The repo will have React, TS, Cypress (e2e & ct), GHA with CI architecture, Jest, ESLint, Prettier, Renovate, Husky, Lint-staged, and most of the things you wish to have before getting started with a new project. Clone your new repo and install.
For the instructions we will assume that the repo you created is https://github.com/muratkeremozcan/tour-of-heroes-react-cypress-ts, where you can find the final version of the app. The examples use yarn , and npm can be used if preferred.
git clone https://github.com/muratkeremozcan/tour-of-heroes-react-cypress-ts
cd tour-of-heroes-react-cypress-ts
# if you are setup on a company proxy, append the --registry modifier
# otherwise just yarn install
yarn install --registry https://registry.yarnpkg.com
# note: from here on assume that --registry https://registry.yarnpkg.com
# will need to be appended if working on a company proxy
# else you will have to host the repo in the company's private GitHub domain
For a sanity check, we will execute the commands one at a time
# parallel unit, typecheck, lint, format, build
yarn validate
# Execute the e2e, ct & unit tests
# check the Cypress component test runner
yarn cy:open-ct
# check the Cypress e2e test runner (starts the app)
yarn cy:open-e2e
# check Jest (local execution is in watch mode)
yarn test
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