Settings Moxinet

Mocking server that, just like mox, allows parallel testing.

Installation

If available in Hex, the package can be installed by adding moxinet to your list of dependencies in mix.exs:

def deps do
  [
    {:moxinet, "~> 0.1.0"}
  ]
end

Usage

To use moxinet you must first define your mock server, from which you'll forward mock-specific requests:

# test/support/mock_server.ex

defmodule MockServer do
  use Moxinet.Server

  forward("/github", to: GithubMock)
end

Start moxinet in test_helper.exs (before ExUnit.start())

{:ok, _} = Moxinet.start()

ExUnit.start()

---

If you're familiar with plug, you'll see that our mock server is indeed a plug and can therefore be extended like one.

After you've added your server, mocks can be defined:

# test/support/mocks/github_mock.ex

defmodule GithubMock do
  use Moxinet.Mock
end

In tests, you can create rules for how your mocks should behave through expect/4:

describe "create_pr/1" do
  test "creates a pull request when" do
    GithubMock.expect(:post, "/pull-requests/123", fn _payload ->
      %{status: 202, body: %{id: "pull-request-id"}}
    end)

    assert {:ok, %{status: 202, body: %{"id" => "pull-request-id"}}}} = GithubAPI.create_pr(title: "My PR")
  end
end

NOTE: One small caveat with moxinet is that in order for us to be able to match a mock defined in a request with an incoming request, the requests must send the x-moxinet-ref header. Most HTTP libraries allows adding custom headers to your requests, but that might not always be the case.

It's also not recommended to send the x-moxinet-ref header outside your test environment, meaning you'd likely want to do find a way to conditionally add it. Here is one example on how to achieve it in req:

defmodule GithubAPI do
  def client do
    Req.new([
      # ...
    ])
    |> add_moxinet_header()
  end

  defmacrop add_moxinet_header(req) do
    if Mix.env() == :test do
      quote do
        {header_name, header_value} = Moxinet.build_mock_header()
      
        Req.Request.put_new_header(unquote(req), header_name, header_value)
      end
    else
      quote do
        unquote(req)
      end
    end
  end
end

How it works

Moxinet works a lot similar to mox except it'll focus on solving the same issue for HTTP request.

The test pid will be registered in the mock registry, where it can later be accessed from inside the mock.

flowchart TD
    TP[Test pid] --> MR[Mock registry]
    GMS <--> MR
    TP --> API[Github API]
    API -.HTTP request.-> MS[Mock server]
    MS --> GMS[Github Mock]
    GMS -.HTTP response.-> API

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/moxinet.