Nowadays many web applications are Single Page Apps that connect to an API via HTTP (for example REST or GraphQL). When you develop such an application, you do not only have to run a local development server, but also an API where it connects to. The API could be running on a dev cluster, but you can also run it locally on a different port for example.
A big advantage of connecting to a real API, is that you probably create less bugs. On the other hand, it is sometimes hard to test or setup up all possible scenarios. How do you for example test, in a controlled way, that your API responds with an internal server error and how the client handles this? In this blog I explain how to do this.