feat: add device group subscription

- add GraphQL subscription for device group creation and updates
- update tests to verify subscription functionality

Signed-off-by: Osman Hadzic <osman.hadzic@secomind.com>

Author: osmanhadzic

backend/lib/edgehog/groups/device_group/device_group.ex

@@ -33,6 +33,14 @@ defmodule Edgehog.Groups.DeviceGroup do
     type :device_group
 
     # TODO: paginate `device` relationship with relay
+
+    subscriptions do
+      pubsub EdgehogWeb.Endpoint
+
+      subscribe :device_group_event do
+        action_types [:create, :update, :destroy]
+      end
+    end
   end
 
   actions do

backend/test/edgehog_web/schema/subscriptions/device_group/device_group_subscriptions_test.exs

@@ -0,0 +1,90 @@
+#
+# This file is part of Edgehog.
+#
+# Copyright 2026 SECO Mind Srl
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+defmodule EdgehogWeb.Schema.Subscriptions.DeviceGroup.DeviceGroupSubscriptionsTest do
+  @moduledoc false
+  use EdgehogWeb.SubsCase
+
+  import Edgehog.GroupsFixtures
+
+  describe "DeviceGroup subscription" do
+    test "receive data on device group creation", %{socket: socket, tenant: tenant} do
+      subscribe(socket)
+
+      device_group = device_group_fixture(tenant: tenant)
+
+      assert_push "subscription:data", push
+
+      assert_device_group_created(device_group_data, push)
+
+      assert device_group_data["id"] == AshGraphql.Resource.encode_relay_id(device_group)
+      assert device_group_data["name"] == device_group.name
+      assert device_group_data["handle"] == device_group.handle
+      assert device_group_data["selector"] == device_group.selector
+    end
+
+    test "receive data on device group update", %{socket: socket, tenant: tenant} do
+      device_group = device_group_fixture(tenant: tenant)
+      subscribe(socket)
+
+      new_name = "new_name_#{System.unique_integer()}"
+
+      device_group
+      |> Ash.Changeset.for_update(:update, %{name: new_name})
+      |> Ash.update!(tenant: tenant)
+
+      assert_push "subscription:data", push
+      assert_device_group_updated(device_group_data, push)
+
+      assert device_group_data["id"] == AshGraphql.Resource.encode_relay_id(device_group)
+      assert device_group_data["name"] == new_name
+      assert device_group_data["handle"] == device_group.handle
+      assert device_group_data["selector"] == device_group.selector
+    end
+  end
+
+  defp subscribe(socket, opts \\ []) do
+    default_sub_gql = """
+    subscription {
+      deviceGroupChanged {
+        created {
+          id
+          name
+          handle
+          selector
+        }
+        updated {
+          id
+          name
+          handle
+          selector
+        }
+      }
+    }
+    """
+
+    sub_gql = Keyword.get(opts, :query, default_sub_gql)
+
+    ref = push_doc(socket, sub_gql)
+    assert_reply ref, :ok, %{subscriptionId: subscription_id}
+
+    subscription_id
+  end
+end

backend/test/support/assertions.ex

@@ -53,4 +53,34 @@ defmodule Edgehog.Assertions do
              } = var!(unquote(push))
     end
   end
+
+  defmacro assert_device_group_created(created_data, push) do
+    quote do
+      assert %{
+               result: %{
+                 data: %{
+                   "deviceGroupChanged" => %{
+                     "created" => var!(unquote(created_data)),
+                     "updated" => nil
+                   }
+                 }
+               }
+             } = var!(unquote(push))
+    end
+  end
+
+  defmacro assert_device_group_updated(updated_data, push) do
+    quote do
+      assert %{
+               result: %{
+                 data: %{
+                   "deviceGroupChanged" => %{
+                     "created" => nil,
+                     "updated" => var!(unquote(updated_data))
+                   }
+                 }
+               }
+             } = var!(unquote(push))
+    end
+  end
 end