ExUnited - Easily spawn Elixir nodes (supervising, Mix configured, easy asserted / refuted) within ExUnit tests

Hi all,

ExUnited is a Hex package designed to easily facilitate spawning supervising local Elixir nodes within tests. Unfortunately, I was not able to properly setup a spawned node for supervisioning with the Erlang :slave.start_link/1 function. So I have written ExUnited to accomplish that, along with supporting Mix.Config configurations, additional loaded code, and a developer friendly way of writing assertions and refutations in the context of a spawned node which really improved the readability of the tests and more.


  • Spawn nodes for testing purposes
  • Spin up “partially connected” vs “fully connected” nodes
  • Run in “verbose” mode which prints a colorized STDOUT of the nodes
  • Specify extra “code paths” which will be included ( config.exs included)
  • Support child supervisioning within a spawned node
  • Exclude certain dependencies for spawned nodes
  • Easily assert and refute within the context of spawned nodes


defmodule MyNodeClusterTest do
  use ExUnited.Case

  setup do
    {:ok, spawned} =
        david: [code_paths: ["test/nodes/beckham"], supervise: [David]]

    on_exit(fn ->


  test "executes code in spawned node", spawned do
    assert :"captain@" = Node.self()
    refute :"david@" == Node.self()
    sentence = "The only time you run out of chances is when you stop taking them."

    as_node(:david, phrase: sentence) do
      assert :"david@" = Node.self()
      refute :"captain@" == Node.self()
      assert ^phrase = David.talk()

      foo = :bar
      refute match?(%{node: ^foo}, %{node: :foo})

See full example.

Enjoy the package! I would love to receive a shoutout and/or your feedback :wink:


I just released ExUnited v0.1.1 containing the following enhancements:

  • Add :exclude option for individual spawned nodes
  • Exclude current project as dependency (instead, add “lib” to code paths)
  • Do not generate config files
  • Fix redundant prompt when in verbose mode

ExUnited v0.1.2 has just been released:

  • Add ability to use a different MIX_ENV when spawning nodes (solves meck related testing problems)
  • Add boolean flag to not start ExUnit

The README fragment concerning the mix_env configuration:

ATTENTION: When also using meck-based packages

The following errors can occur when also using packages like mock or MecksUnit (which both use the Erlang library meck to mock functions) and spawning the nodes with the default environment test:

  • (UndefinedFunctionError) function Some.Module.some_function/1 is undefined
  • (ErlangError) Erlang error: {{:undefined_module, < Some.Module >}

To tackle this, you should configure any other (Mix) environment to spawn the nodes with. Configure it like so:

# config/test.exs
import Config

config :ex_united,
  mix_env: :dev

You might also want to consider using a bogus environment (e.g. :void) to skip the non-relevant :dev dependencies, like credo or dialyxir probably. That will save some compile time.

And last but not least, please note that using a different environment within CI builds will require compiling the project in that particular environment on beforehand of the tests. Otherwise spawning the nodes will take too much time and that will cause timeout errors during the tests.

# .gitlab-ci.yml
  - MIX_ENV=void mix deps.get
  - MIX_ENV=void mix run -e 'IO.puts("Done.")'
  - epmd -daemon
  - mix test