Commanded provides an in-memory event store implementation, for test use only, in the module Commanded.EventStore.Adapters.InMemory. This is a transient event store without persistence.

Ensure you configure the in-memory adapter in your environment config file, config/test.exs:

config :my_app, MyApp.App,
  event_store: [
    adapter: Commanded.EventStore.Adapters.InMemory,
    serializer: Commanded.Serialization.JsonSerializer
  ]

You may replace or omit the serializer configuration. By including it here we ensure events used by the tests can be successfully serialized and deserialized.

You can use ExUnit's case template feature to restart the in-memory event store for each test run.

defmodule InMemoryEventStoreCase do
  use ExUnit.CaseTemplate
  alias Commanded.EventStore.Adapters.InMemory
  setup do
    {:ok, _apps} = Application.ensure_all_started(:my_app)
    on_exit(fn ->
      :ok = Application.stop(:my_app)
    end)
  end
end

Replace both occurrences of :my_app in the above ExUnit case template with the name of your own application.

The reason why your app must be stopped and then started between resetting the event store is to ensure all application processes are restarted with their initial state to prevent state from one test affecting another.

Use the InMemoryEventStoreCase module within any test files that need to use the event store.

defmodule ExampleTest do
  use InMemoryEventStoreCase
  # Define your tests here ...
end

Run mix test as usual to execute the tests using the in-memory event store.