[samselikoff]

Great question! When I started Mirage this was the biggest concern, but after years of usage it turns out to not be that big of a deal in practice. Said another way, the benefits of being able to easily write high-level UI tests for a variety of server states all within your frontend codebase outweigh the costs of potential false positives. Also, teams don't break their HTTP APIs that often.

Even so, there are teams that have used tools like Pact to perform contract testing, ensuring their Mirage server and their production API never fall out of sync. Even more exciting to me would be using something like Typescript to verify the API contract at compile-time (also something that others have been exploring).

As far as only running Mirage during development, the Ember addon does this but we need to document how to do this in the general case. When you build your app for production Mirage should not be in any application code, nor should the miragejs library be included in your bundle. Webpack is capable of this, we just need to document it.

Mirage is flexible enough to match any backend API – this is where it shines in comparison to tools like json-server. With Mirage the goal is to mock out your exact production API; its serializers and route handlers can be customized to match any API format. Often teams using Mirage reach agreement about the shape of their API beforehand, precisely so that the frontend team can move and build the UI without having to wait on the API to be ready.

Indeed, Mirage can even be thought of as a communication tool that helps impose conventions and consistency on the API layer, making both the frontend developers and the backend developers happier.