This approach works, but consider using a specific key in config like config :my_app, :whatever_the_feature_is_called and enabling / disabling that in files like config/test.exs etc - coupling everything to a generic “environment” option makes it harder to see what options vary per-environment.

In case anyone is searching in the future, I found another answer for this:

1. Add some kind of environment setting in your various config files (dev.exs, prod.exs, test.exs):

  config :my_app, :environment, :prod

2. In your router (and in my case, nav code in templates) you can then inspect that setting

  if Application.get_env(:my_app, :environment) in [:dev, :test] do
    ...

seems to work ok - I have checked running using mix & a release.

Not the answer you may be looking for but at work we just restrict the /graphiql route to users that are logged in as company admins which you can accomplish with a simple plug. Plus graphiql doesn’t really expose anything that isn’t already exposed via the GraphQL api itself.