# `DDD.Test`
[🔗](https://github.com/blackuprise/vicander/blob/v0.1.1/lib/ddd/operations/test.ex#L1)

Helpers for testing an application built on the framework.

    use ExUnit.Case
    import DDD.Test

    test "completing the last item finishes the list" do
      {:ok, list} = TodoList.complete_item(list, item.id)

      assert_event_emitted(list, ItemCompleted, item_id: item.id)
      refute_event_emitted(list, ListReopened)
    end

    test "a failure says why" do
      assert_error_code(TodoList.complete_item(list, item.id), :already_completed)
    end

    test "the handlers ran" do
      {:ok, _} = Commands.AddItem.call(...)
      drain_outbox()
      assert ... # the handlers' effects
    end

Pending events are the ones an aggregate has emitted and not yet saved. Once a repository
saves it they are in the outbox; `drain_outbox/1` delivers them to the subscribed handlers.

# `assert_error_code`

```elixir
@spec assert_error_code(term(), atom()) :: DDD.Error.t()
```

Assert that a result is `{:error, %DDD.Error{}}` that has `code` (its own, or one of its
violations'). Returns the error, so more can be asserted about it.

# `assert_event_emitted`

```elixir
@spec assert_event_emitted(struct(), module(), keyword()) :: struct()
```

Assert that `aggregate` emitted an event of the `event` module, optionally with these field
values. Returns the first matching event.

# `drain_outbox`

```elixir
@spec drain_outbox(non_neg_integer()) :: non_neg_integer()
```

Deliver every event waiting in the outbox to the subscribed handlers, now, instead of waiting
for the poller's timer. Needs the poller to be running (`DDD.Supervisor` starts it, with
`poller: [interval_ms: 600_000]` to keep it from polling by itself in tests). Events that
handlers produce while handling are delivered too. Returns how many events were delivered.

# `emitted_events`

```elixir
@spec emitted_events(struct()) :: [struct()]
```

The events an aggregate has emitted and not yet saved.

# `refute_event_emitted`

```elixir
@spec refute_event_emitted(struct(), module(), keyword()) :: :ok
```

Assert that `aggregate` did not emit such an event.

---

*Consult [api-reference.md](api-reference.md) for complete listing*