I mentioned the concept of technical debt in the previous chapter, which, as a reminder, is the building up of work that must be done before a particular job is complete, making changes much harder to implement in the future. A codebase without tests is a clear indication of a technical debt. Let's explore this statement in more detail.
Even very simple applications will generally comprise of the following:
Features, which the end user interacts with
Shared services such as authentication and authorization that features interact with
These will all generally depend on some direct persistent storage, or API. And finally, for implementing most of these features and services, we will use libraries, frameworks, and modules, regardless of language. So even for simpler applications, we have arrived at a few dependencies to manage already, where a breaking change in one could possibly break everything up in the chain.
So let's take a common use case in which...
