diff --git a/test/federation/activity_pub/types/events_test.exs b/test/federation/activity_pub/types/events_test.exs
index f2f934461..2da5def62 100644
--- a/test/federation/activity_pub/types/events_test.exs
+++ b/test/federation/activity_pub/types/events_test.exs
@@ -5,7 +5,8 @@ defmodule Mobilizon.Federation.ActivityPub.Types.EventsTest do
 
   alias Mobilizon.Actors.Actor
   alias Mobilizon.Events
-  alias Mobilizon.Events.Event
+  alias Mobilizon.Events.{Event, Participant}
+  alias Mobilizon.Federation.ActivityPub.Activity
   alias Mobilizon.Federation.ActivityPub.Types.Events
 
   @ap_public "https://www.w3.org/ns/activitystreams#Public"
@@ -266,5 +267,174 @@ defmodule Mobilizon.Federation.ActivityPub.Types.EventsTest do
                data
              )
     end
+
+    test "from a remote group member" do
+      %Actor{id: organizer_actor_1_id, url: actor_1_url} = actor_1 = insert(:actor)
+      %Actor{} = actor_2 = insert(:actor)
+
+      %Actor{
+        url: group_url,
+        followers_url: followers_url,
+        members_url: members_url
+      } = group = insert(:group, domain: "somewhere.else", url: "https://somewhere.else/@someone")
+
+      insert(:member, parent: group, actor: actor_1, role: :moderator)
+      insert(:member, parent: group, actor: actor_2, role: :moderator)
+
+      {:ok, begins_on, _} = DateTime.from_iso8601(@event_begins_on)
+
+      %Event{} =
+        event =
+        insert(:event, organizer_actor: actor_2, begins_on: begins_on, attributed_to: group)
+
+      assert {:ok, %Event{}, data} =
+               Events.update(
+                 event,
+                 Map.merge(@event_update_data, %{
+                   organizer_actor_id: organizer_actor_1_id
+                 }),
+                 %{}
+               )
+
+      assert match?(
+               %{
+                 "actor" => ^actor_1_url,
+                 "attributedTo" => ^group_url,
+                 "cc" => [^members_url, ^followers_url],
+                 "object" => %{
+                   "actor" => ^actor_1_url,
+                   "anonymousParticipationEnabled" => false,
+                   "attributedTo" => ^group_url,
+                   "cc" => [],
+                   "commentsEnabled" => false,
+                   "draft" => false,
+                   "ical:status" => "CONFIRMED",
+                   "joinMode" => "free",
+                   "maximumAttendeeCapacity" => nil,
+                   "mediaType" => "text/html",
+                   "name" => @event_updated_title,
+                   "repliesModerationOption" => nil,
+                   "startTime" => @event_begins_on,
+                   "tag" => [],
+                   "to" => [@ap_public],
+                   "type" => "Event"
+                 },
+                 "to" => [@ap_public],
+                 "type" => "Update"
+               },
+               data
+             )
+    end
+  end
+
+  describe "join an event" do
+    test "simple and remote" do
+      %Actor{url: organizer_actor_url} =
+        organizer_actor = insert(:actor, domain: "somewhere.else")
+
+      %Actor{url: participant_actor_url} = actor = insert(:actor, domain: nil)
+
+      %Event{url: event_url} =
+        event = insert(:event, organizer_actor: organizer_actor, local: false)
+
+      assert {:ok, data, %Participant{}} = Events.join(event, actor, true, %{})
+
+      assert match?(
+               %{
+                 "actor" => ^participant_actor_url,
+                 "cc" => [],
+                 "object" => ^event_url,
+                 "participationMessage" => nil,
+                 "to" => [^participant_actor_url, ^organizer_actor_url],
+                 "type" => "Join"
+               },
+               data
+             )
+    end
+
+    test "simple and local" do
+      %Actor{url: organizer_actor_url} = organizer_actor = insert(:actor, domain: nil)
+
+      %Actor{url: participant_actor_url} = actor = insert(:actor, domain: nil)
+
+      %Event{url: event_url} = event = insert(:event, organizer_actor: organizer_actor)
+
+      assert {:accept, {:ok, %Activity{data: data, local: true}, %Participant{}}} =
+               Events.join(event, actor, true, %{})
+
+      assert match?(
+               %{
+                 "actor" => ^organizer_actor_url,
+                 "cc" => [],
+                 "object" => %{
+                   "actor" => ^participant_actor_url,
+                   "object" => ^event_url,
+                   "participationMessage" => nil,
+                   "type" => "Join"
+                 },
+                 "to" => [^participant_actor_url, ^organizer_actor_url],
+                 "type" => "Accept"
+               },
+               data
+             )
+    end
+
+    test "group event local" do
+      %Actor{url: organizer_group_url, members_url: members_url, followers_url: followers_url} =
+        organizer_group = insert(:group, domain: nil)
+
+      %Actor{url: participant_actor_url} = actor = insert(:actor, domain: nil)
+
+      %Event{url: event_url} = event = insert(:event, attributed_to: organizer_group)
+
+      assert {:ok, data, %Participant{}} = Events.join(event, actor, true, %{})
+
+      assert match?(
+               %{
+                 "actor" => ^participant_actor_url,
+                 "cc" => [^followers_url, ^members_url],
+                 "object" => ^event_url,
+                 "participationMessage" => nil,
+                 "to" => [^participant_actor_url, ^organizer_group_url],
+                 "type" => "Join"
+               },
+               data
+             )
+    end
+
+    test "group event with organizer remote" do
+      %Actor{url: organizer_group_url, members_url: members_url, followers_url: followers_url} =
+        organizer_group = insert(:group, domain: nil)
+
+      %Actor{url: organizer_actor_url} =
+        organizer_actor =
+        insert(:actor, domain: "somewhere.else", url: "https://somewhere.else/@someone")
+
+      insert(:member, parent: organizer_group, actor: organizer_actor, role: :moderator)
+
+      %Actor{url: participant_actor_url} = actor = insert(:actor, domain: nil)
+
+      %Event{url: event_url} =
+        event =
+        insert(:event,
+          attributed_to: organizer_group,
+          organizer_actor: organizer_actor,
+          local: true
+        )
+
+      assert {:ok, data, %Participant{}} = Events.join(event, actor, true, %{})
+
+      assert match?(
+               %{
+                 "actor" => ^participant_actor_url,
+                 "cc" => [^followers_url, ^members_url],
+                 "object" => ^event_url,
+                 "participationMessage" => nil,
+                 "to" => [^participant_actor_url, ^organizer_group_url],
+                 "type" => "Join"
+               },
+               data
+             )
+    end
   end
 end