I haven’t read the details of everything in this thread but in summary Raxx has a few opinions about these things.
Configuration is passed in at boot time of a server, that handles the problem of having to do stuff on every request, but it is entirely up to the developer what shape of stuff is in config. I normally have a MyApp.Config struct and that module has setup function that will create a struct by whatever means necessary (e.g. pulling env variables).
For testing I start a separate server for each test so have the option to override any config value for the duration of the test.
I haver personally never made business logic configurable, but most side effect things that the business logic needs are passed in, e.g. sending emails, calling third party apis, db access (sometimes).
Normally I don’t test at the business logic/interaction layer but instead I have a lot of tests that create requests, pass them to the endpoint and assert on the response.
def handle_request(%{method: :GET, path: []}, config) do
MyApp.BusinessAction.create(data_from_request, config.mailer)
response(:ok)
end
Hope that’s helpful. It might be time for me to write a blog post about some of these things, but on the other hand I don’t feel my web layer needs to prescribe anything about how the various pieces of the whole application are composed together.