Inject

Inject is a library that lets you write testable Elixir code that can run concurrently in ExUnit.

Installation

def deps do
  [
    {:inject, "~> 0.4.0"}
  ]
end

It is recommended to disable inject in prod.exs to avoid any performance penalty for registry lookups.

config :inject, disabled: true

Usage

Inject is just a couple of functions.

• inject/1 aliased as i/1. Use this function in your implementation code to flag modules for potential injection.

defmodule MyApplication do
  import Inject, only: [i: 1]

  def process do
    {:ok, file} = i(File).open("your-mind.txt", [])
    ...
  end
end

• register/2 register/3. Use this function in your tests to register a stubbed implementation for a module.

defmodule MyApplicationTest do
  use ExUnit.Case, async: true
  import Inject, only: [register: 2]

  defmodule FileStub do
    def open("your-mind.txt", _opts) do
      {:ok, nil}
    end
  end

  test "use my stub for this test" do
    register(File, FileStub)
    {:ok, nil} = MyApplication.process()
  end
end

Defining stubbed modules like this is great, but I like to pair Inject w/ Double for on-the-fly setups.

defmodule MyApplicationTest do
  use ExUnit.Case, async: true
  import Inject, only: [register: 2]
  import Double

  test "use my stub for this test" do
    register(File, stub(File, :open, fn(_, _) -> {:ok, nil} end))
    {:ok, nil} = MyApplication.process()
  end
end

Shared Mode

If you want to inject a dependency that will be shared by all processes, you can do so by passing the shared: true option. This can be useful if you have background processing. This is only recommended for tests that do not run async.

register(File, FileStub, shared: true)

TODO

• Add allow/1 for enabling another process to use registrations from the current test.