test: cover MobileController format_equipment_details interface mapping

Adds direct call to MobileController.get_device with a snmp_device that
has interfaces — drives the Enum.map over interfaces in
format_equipment_details that previously had no fixture coverage.

test/towerops_web/controllers/api/mobile_controller_test.exs

@@ -208,6 +208,54 @@ defmodule ToweropsWeb.Api.MobileControllerTest do
       assert is_list(body["sensors"])
       assert body["uptime"] =~ "h"
     end
+
+    test "get_device direct call maps interfaces when SNMP device has them",
+         %{user: user, organization: org} do
+      alias Towerops.Snmp.Interface
+      alias ToweropsWeb.Api.MobileController
+
+      {:ok, site} =
+        Towerops.Sites.create_site(%{name: "Iface Site", organization_id: org.id})
+
+      {:ok, device} =
+        Towerops.Devices.create_device(%{
+          name: "WithIfaces",
+          ip_address: "10.55.55.55",
+          site_id: site.id,
+          organization_id: org.id,
+          snmp_enabled: true
+        })
+
+      {:ok, snmp_dev} =
+        Towerops.Repo.insert(%Device{
+          device_id: device.id,
+          sys_uptime: 5_000,
+          sys_descr: "test"
+        })
+
+      {:ok, _iface} =
+        Towerops.Repo.insert(%Interface{
+          snmp_device_id: snmp_dev.id,
+          if_index: 1,
+          if_name: "ge-0/0/0",
+          if_alias: "uplink",
+          if_oper_status: "up",
+          if_admin_status: "up",
+          if_speed: 1_000_000_000,
+          if_phys_address: "aa:bb:cc:dd:ee:ff"
+        })
+
+      conn = Plug.Conn.assign(build_conn(), :current_user, user)
+      conn = MobileController.get_device(conn, %{"id" => device.id})
+
+      assert conn.status == 200
+      body = Jason.decode!(conn.resp_body)
+      assert [iface] = body["interfaces"]
+      assert iface["name"] == "ge-0/0/0"
+      assert iface["alias"] == "uplink"
+      assert iface["status"] == "up"
+      assert iface["mac_address"] == "aa:bb:cc:dd:ee:ff"
+    end
   end
 
   describe "list_alerts — formatting" do