update switch provider scheduled task

it now looks at both providers and works out whether to deprioritise
one, rather than binary switching from one to the other. If anything
has altered the priorities in the last ten minutes it won't take any
action. If both providers are slow it also won't take any action.

tests/app/celery/test_scheduled_tasks.py

@@ -15,11 +15,13 @@ from app.celery.scheduled_tasks import (
     replay_created_notifications,
     check_precompiled_letter_state,
     check_templated_letter_state,
-    check_for_missing_rows_in_completed_jobs
+    check_for_missing_rows_in_completed_jobs,
+    switch_current_sms_provider_on_slow_delivery,
 )
 from app.config import QueueNames, TaskNames
 from app.dao.jobs_dao import dao_get_job_by_id
 from app.dao.notifications_dao import dao_get_scheduled_notifications
+from app.dao.provider_details_dao import get_provider_details_by_notification_type, get_provider_details_by_identifier
 from app.models import (
     JOB_STATUS_IN_PROGRESS,
     JOB_STATUS_ERROR,
@@ -98,13 +100,61 @@ def test_should_update_all_scheduled_jobs_and_put_on_queue(sample_template, mock
     ])
 
 
-def test_switch_providers_on_slow_delivery_switches_once_then_does_not_switch_if_already_switched(
-        notify_api,
-        mocker,
-        sample_user,
-        sample_template
+@freeze_time('2017-05-01 14:00:00')
+def test_switch_current_sms_provider_on_slow_delivery_switches_when_one_provider_is_slow(
+    mocker,
+    restore_provider_details,
 ):
-    raise NotImplementedError  # TODO
+    is_slow_dict = {'mmg': False, 'firetext': True}
+    mock_is_slow = mocker.patch('app.celery.scheduled_tasks.is_delivery_slow_for_providers', return_value=is_slow_dict)
+    mock_reduce = mocker.patch('app.celery.scheduled_tasks.dao_reduce_sms_provider_priority')
+    # updated_at times are older than the 10 minute window
+    get_provider_details_by_identifier('mmg').updated_at = datetime(2017, 5, 1, 13, 49)
+    get_provider_details_by_identifier('firetext').updated_at = None
+
+    switch_current_sms_provider_on_slow_delivery()
+
+    mock_is_slow.assert_called_once_with(
+        threshold=0.3,
+        created_at=datetime(2017, 5, 1, 13, 50),
+        delivery_time=timedelta(minutes=4)
+    )
+    mock_reduce.assert_called_once_with('firetext')
+
+
+@freeze_time('2017-05-01 14:00:00')
+def test_switch_current_sms_provider_on_slow_delivery_does_nothing_if_recent_changes(
+    mocker,
+    restore_provider_details,
+):
+    mock_is_slow = mocker.patch('app.celery.scheduled_tasks.is_delivery_slow_for_providers')
+    mock_reduce = mocker.patch('app.celery.scheduled_tasks.dao_reduce_sms_provider_priority')
+    get_provider_details_by_identifier('mmg').updated_at = datetime(2017, 5, 1, 13, 51)
+
+    switch_current_sms_provider_on_slow_delivery()
+
+    assert mock_is_slow.called is False
+    assert mock_reduce.called is False
+
+
+@freeze_time('2017-05-01 14:00:00')
+@pytest.mark.parametrize('is_slow_dict', [
+    {'mmg': False, 'firetext': False},
+    {'mmg': True, 'firetext': True},
+])
+def test_switch_current_sms_provider_on_slow_delivery_does_nothing_if_no_need(
+    mocker,
+    restore_provider_details,
+    is_slow_dict
+):
+    mocker.patch('app.celery.scheduled_tasks.is_delivery_slow_for_providers', return_value=is_slow_dict)
+    mock_reduce = mocker.patch('app.celery.scheduled_tasks.dao_reduce_sms_provider_priority')
+    get_provider_details_by_identifier('mmg').updated_at = datetime(2017, 5, 1, 13, 51)
+
+
+    switch_current_sms_provider_on_slow_delivery()
+
+    assert mock_reduce.called is False
 
 
 @freeze_time("2017-05-01 14:00:00")