Affiliate Service Dependency System

dependency_system.ex

# A module that uses dependencies
defmodule EventStore.MyModule do
  defp stream_filterer, do: EventStore.Dependencies.get(:stream_filterer)

  def something do
    stream_filterer.do_the_things
  end
end

# A test for the module that uses dependencies
defmodule EventsStore.MyModuleTest do
  defmodule FakeStreamFilterer do
    def do_the_things do
      # ...
    end
  end

  test "it does the right stuff" do
    EventStore.Mocks.update(:stream_filterer, FakeStreamFilterer)

    #...
  end
end

supporting_files.ex

# config
config :event_store, :dependencies,
  stream_filterer: EventStore.StreamFilterer

# dependency module
# Just wraps `Application.fetch_env`
defmodule EventStore.Dependencies do
  def get(key), do: config[key]

  defp config do
    Application.fetch_env!(:event_store, :dependencies)
  end
end

# A example dependency
defmodule EventStore.StreamFilterer do
  def do_the_things do
    # ...
  end
end

# The test Helper that updates dependencies
defmodule EventsStore.Mocks do
  def update(key, module) do
    # Updates the appropriate config
    # Ensures the config resets after the test
    # Ensures that the module you are swapping in has the same functions as the default module
  end
end