The differences between frontend and backend

TDD as a practice does not differentiate client-side applications from server-side applications, writing test first is a practice that goes beyond that. Investigating the literature on that topic shows that the first books that came about were in Java, which is also known as a server-side language that happens to support some of the client-side features. However, as TDD became ubiquitous to other stacks the differences between server and client started to become more apparent.

For some, the idea of testing client-side applications is a waste of time and there is no need to invest time on it as the user interface that is built is just an “implementation detail”. I would attribute such misunderstanding to one of the books that is a reference in software architecture: Clean Architecture by Uncle Bob. In the book, the UI is treated as something not important and doesn´t deserve attention. The book was released in 2017 and since then the industry has evolved the reality is that the client-side applications started to have a set of tools to write tests first just for them.

QUnit for example is the testing framework for jQuery one of the libraries most popular to date. jest/mocha for more recent applications and jasmine for the angular ecosystem. ReactJs and testing-library became the power duet for writing testable code in the front end. VueJs and Angular also have a representative ecosystem.

It is also necessary to understand that server-side applications have different roles and responsibilities in comparison with client-side applications. The client side is often interested in responsiveness, browser APIs, async state and avoiding freezing, whereas server-side applications are interested in the interaction with the storage system, HTTP requests, queues and queues.