Commanded.ProcessManagers.ProcessManager.identity/0 function returns nil in unit tests

[jvantuyl]

When doing unit tests of process manager callback modules, the Commanded.ProcessManagers.ProcessManager.identity/0 function returns nil. It's easy enough to set the identity during the test with Process.put(:process_uuid, id), but that builds tests that rely on the internals of Commanded.

It would be useful to have a test helper that can be used with ExUnit.Callbacks.setup/1 like this:

defmodule Commanded.TestHelpers do
  def with_process_manager_identity(id, _context) do
    Process.put(:process_uuid, id)
  end
end

And we could use it in tests like this:

defmodule MyAppTest.SomeTest do
  use MyAppTest.Case, async: true
  # MyApp.TestCase impots Commanded.TestHelpers

  setup do
    with_process_manager_identity "my_uuid"
  end
end