Using Test Doubles With Server Apps

While writing tests for server apps, your language/framework no doubt provides facilities for providing test-doubles for code within your project.

As is the theme in this content, though, we are going to primarily look at ways to use test-doubles for backing services, like databases, APIs, and message brokers.

These will run out-of-process from our application, and we will be communicating with them with the same mechanisms we would ultimately be using in production. E.g. we will make real HTTP requests to other APIs, use real databases (not "in memory" stand ins), and talk to real message brokers.

The end result (and this is the goal of the browser-based test doubles presented here as well) is that the only thing that will change about our application from running locally, being tested in our pipeline or a staging environment, and in production is the configuration.

Configuration is What Defines an Environment

Maybe a bit overstated, but our goal is to not have different builds of our application running in different environments.