Make inbox page update using AJAX

Fairly self-explanatory. Uses the same pattern of breaking things up
into functions as the jobs page.

tests/app/main/views/test_dashboard.py

@@ -1,3 +1,4 @@
+import json
 from functools import partial
 import copy
 from unittest.mock import call, ANY
@@ -220,6 +221,30 @@ def test_anyone_can_see_inbox(
     )
 
 
+def test_view_inbox_updates(
+    logged_in_client,
+    service_one,
+    mocker,
+    mock_get_inbound_sms_with_no_messages,
+):
+
+    service_one['permissions'] = ['inbound_sms']
+
+    mock_get_partials = mocker.patch(
+        'app.main.views.dashboard.get_inbox_partials',
+        return_value={'messages': 'foo'},
+    )
+
+    response = logged_in_client.get(url_for(
+        'main.inbox_updates', service_id=SERVICE_ONE_ID,
+    ))
+
+    assert response.status_code == 200
+    assert json.loads(response.get_data(as_text=True)) == {'messages': 'foo'}
+
+    mock_get_partials.assert_called_once_with(SERVICE_ONE_ID)
+
+
 def test_should_show_recent_templates_on_dashboard(
     logged_in_client,
     mocker,