Injexor provides an easy way to replace modules based on behaviours for mocking during tests or stubbing in another module based on config for different environments.

See the docs for full instructions: https://hexdocs.pm/injexor

The package can be installed by adding injexor to your list of dependencies in mix.exs:

def deps do
  [
    {:injexor, "~> 1.0.0"}
  ]
end

• test.exs

  config :injexor, default: Mock # adds Mock on the end of all modules by default
  
  # or you can alternatively register injects manually
  config :injexor, MyApp.MyBehaviour, inject: MyApp.Mock

• test_helper.exs

  Hammox.defmock(MyApp.Mock, for: MyApp.MyBehaviour)

• lib/my_app.ex

  defmodule MyApp do
    @behaviour MyApp.MyBehaviour
  
    def deploy_context() do
      Application.fetch_env!(:my_app, :deploy_context)
    end
  end

• lib/my_app/my_behaviour.ex

  defmodule  MyApp.MyBehaviour do
    @callback deploy_context() :: atom()
  end

• lib/my_app/module.ex

  defmodule MyApp.Module do
    use Injexor, inject: [MyApp]
  
    def my_function do
      # you can now use mox/hammox to stub/expect this function to test the different paths
      if MyApp.deploy_context() == "production" do
        # do something
      else
        # do something else
      end
    end
  end