Hi everyone,

I wanted to share rewire with you, a dependency injection library I’ve been working on over the last few weeks. It aims to keep your production code free from testing concerns, works with async tests and any mock.

Example

Given a module such as this:

# this module has a hard-wired dependency on the `English` module
defmodule Conversation do
  def start(), do: English.greet()
end

If you define a mox mock EnglishMock you can rewire the dependency in your unit test:

defmodule MyTest do
  use ExUnit.Case
  use Rewire                                     # (1) activate `rewire`
  import Mox

  rewire Conversation, English: EnglishMock      # (2) rewire `English` to `EnglishMock`

  test "start/0" do
    stub(EnglishMock, :greet, fn -> "g'day" end)
    assert Conversation.start() == "g'day"       # (3) test using the mock
  end
end

Check out all the details at:
https://github.com/stephanos/rewire

And let me know what you think!