Send one-off messages as fast as possible

The vast majority of messages that are being sent one-off are
time-sensitive. A typical example is a caseworker on the phone who sends
a message at the end of the call. They normally wait until the message
has been delivered, so all the time they’re waiting is time when they
can’t be helping someone else.

What we don’t want to happen is for the messages they’re sending to get
stuck behind a big lump of GOV.UK Subscription emails or passport
reminder texts. I think the best way to do this is shift them onto the
priority queue.

We’re currently seeing queue sizes of up to 5,000 on the ‘normal’
queues; I don’t think there’s any risk of this change making the
priority queue more heavily-laden than this. Especially since the
traffic patterns of users sending one-off messages won’t be spiky.

tests/app/service/test_send_one_off_notification.py

@@ -60,7 +60,7 @@ def test_send_one_off_notification_calls_celery_correctly(persist_mock, celery_m
     celery_mock.assert_called_once_with(
         notification=persist_mock.return_value,
         research_mode=False,
-        queue=None
+        queue=QueueNames.PRIORITY,
     )
 
 
@@ -110,7 +110,7 @@ def test_send_one_off_notification_honors_research_mode(notify_db_session, persi
     assert celery_mock.call_args[1]['research_mode'] is True
 
 
-def test_send_one_off_notification_honors_priority(notify_db_session, persist_mock, celery_mock):
+def test_send_one_off_notification_maintains_priority(notify_db_session, persist_mock, celery_mock):
     service = create_service()
     template = create_template(service=service)
     template.process_type = PRIORITY
@@ -231,7 +231,7 @@ def test_send_one_off_notification_should_add_email_reply_to_text_for_notificati
     celery_mock.assert_called_once_with(
         notification=notification,
         research_mode=False,
-        queue=None
+        queue=QueueNames.PRIORITY,
     )
     assert notification.reply_to_text == reply_to_email.email_address
 
@@ -251,7 +251,7 @@ def test_send_one_off_letter_notification_should_use_template_reply_to_text(samp
     celery_mock.assert_called_once_with(
         notification=notification,
         research_mode=False,
-        queue=None
+        queue=QueueNames.PRIORITY,
     )
 
     assert notification.reply_to_text == "Edinburgh, ED1 1AA"
@@ -277,7 +277,7 @@ def test_send_one_off_sms_notification_should_use_sms_sender_reply_to_text(sampl
     celery_mock.assert_called_once_with(
         notification=notification,
         research_mode=False,
-        queue=None
+        queue=QueueNames.PRIORITY,
     )
 
     assert notification.reply_to_text == "447123123123"
@@ -303,7 +303,7 @@ def test_send_one_off_sms_notification_should_use_default_service_reply_to_text(
     celery_mock.assert_called_once_with(
         notification=notification,
         research_mode=False,
-        queue=None
+        queue=QueueNames.PRIORITY,
     )
 
     assert notification.reply_to_text == "447123123456"