Phoenix.LiveViewTest.refute_push_event/4 (#3490)

* Phoenix.LiveViewTest.refute_push_event/4

Adds the `refute_receive` equivalent to `assert_push_event`.

Errors look like:

```elixir
  1) test it can refute events
     test/example_test.exs
     Unexpectedly received event "scores"

     Payload:
     %{points: 100, user: "Dave"}

     (which matched %{points: _, user: "josé"})

     code: refute_push_event(live, "scores", %{points: _, user: "josé"})
     stacktrace:
       test/example_test.exs:273: (test)
```
---------

Co-authored-by: Chris McCord <chris@chrismccord.com>

lib/phoenix_live_view/test/live_view_test.ex

@@ -1613,6 +1613,41 @@ defmodule Phoenix.LiveViewTest do
     end
   end
 
+  @doc """
+  Refutes an event will be pushed within timeout.
+  
+  The default `timeout` is [ExUnit](https://hexdocs.pm/ex_unit/ExUnit.html#configure/1)'s
+  `refute_receive_timeout` (100 ms).
+
+  ## Examples
+
+      refute_push_event view, "scores", %{points: _, user: "josé"}
+  """
+  defmacro refute_push_event(
+             view,
+             event,
+             payload,
+             timeout \\ Application.fetch_env!(:ex_unit, :refute_receive_timeout)
+           ) do
+    quote do
+      %{proxy: {ref, _topic, _}} = unquote(view)
+
+      receive do
+        {^ref, {:push_event, unquote(event), unquote(payload) = data}} ->
+          flunk("""
+          Unexpectedly received event "#{unquote(event)}"
+
+          Payload:
+
+          #{inspect(data, pretty: true)}
+          """)
+      after
+        unquote(timeout) ->
+          false
+      end
+    end
+  end
+
   @doc """
   Asserts a hook reply was returned from a `handle_event` callback.
 

test/phoenix_live_view/integrations/event_test.exs

@@ -69,9 +69,18 @@ defmodule Phoenix.LiveView.EventTest do
       )
 
       assert_push_event(view, "my-event", %{two: 2})
+
       assert render(view) =~ "count: 0"
     end
 
+    test "sends no events if none are pushed", %{conn: conn} do
+      {:ok, view, _html} = live(conn, "/events")
+
+      GenServer.call(view.pid, {:run, fn socket -> {:reply, :ok, socket} end})
+
+      refute_push_event(view, "my-event", _)
+    end
+
     test "sends updates in root and child mounts", %{conn: conn} do
       {:ok, view, _html} = live(conn, "/events-in-mount")
 

test/support/live_views/events.ex

@@ -19,6 +19,10 @@ defmodule Phoenix.LiveViewTest.Support.EventsLive do
     {:reply, reply, socket}
   end
 
+  def handle_event("dont-reply", _, socket) do
+    {:noreply, socket}
+  end
+
   def handle_call({:run, func}, _, socket), do: func.(socket)
 
   def handle_info({:run, func}, socket), do: func.(socket)