Real-World Event Sourcing

Testing Process Managers

Process managers are the inverse of aggregates. A process manager ingests events and produces commands that can either advance or terminate a process. This means that the pure function for a process manager is this:

f(state, event) = c0...cn

The process manager is given its state and a new event and it can then return 0 or more commands. Let’s take a look at an example from a variant of Lunar Frontiers where you want to ensure that the construction process manager requests the spawning of a new building when a construction site is finished.

defmodule ConstructionProcessTest do
  use ExUnit.Case

  test "process manager spawns buildings" do
    input = %{event_type: :construction_completed,
              site_x: ...