What's best practice for feature testing Rails workers with a Redis cache?

Question

In our app's config/environments/development.rb we have

Rails.application.configure do
  # ...
  if ENV['REDIS_URL']
    config.cache_store = :redis_store, ENV['REDIS_URL'], { expires_in: 90.minutes }
  end
end

and in config/environments/test.rb this:

Rails.application.configure do
  # ...
  config.cache_store = :null_store
end

We use some background processes methods in the app, eg:

class UserMailer < ApplicationMailer
  # stuff
end

# ...and elsewhere:

class ProfilesController < ApplicationController
  # stuff
  def amend_confirmation
    # more stuff
    UserMailer.increased_pledge(amendment).deliver_later
  end
end

And when this gets hit in tests, if I don't actively have Redis running in the background (which seems awkward to arrange and potentially buggy to set up in our CI environment), I get the error

Error connecting to Redis on 127.0.0.1:6379 (Errno::ECONNREFUSED) (Redis::CannotConnectError)

For the time being I'm going to deal with this by just mocking/testing for the deliver_later message, but I suspect this isn't a great strategy for a feature test, since it obviously isn't what the user will be doing. Is there a better approach?