Send zendesk ticket when services found with high failure rates

tests/app/service/test_statistics.py

@@ -6,12 +6,13 @@ from freezegun import freeze_time
 import pytest
 
 from app.service.statistics import (
-    format_admin_stats,
-    format_statistics,
+    add_monthly_notification_status_stats,
+    create_empty_monthly_notification_status_stats_dict,
     create_stats_dict,
     create_zeroed_stats_dicts,
-    create_empty_monthly_notification_status_stats_dict,
-    add_monthly_notification_status_stats
+    format_admin_stats,
+    format_statistics,
+    get_rate_of_permanent_failures_for_service
 )
 
 StatsRow = collections.namedtuple('row', ('notification_type', 'status', 'count'))
@@ -73,6 +74,32 @@ def test_format_statistics(stats, email_counts, sms_counts, letter_counts):
     }
 
 
+@pytest.mark.idparametrize("statistics, expected_result", {
+    'counts_rate_for_sms': ([
+        StatsRow('sms', 'permanent-failure', 100),
+        StatsRow('sms', 'delivered', 300),
+    ], 0.25),
+    'ignores_other_notification_types': ([
+        StatsRow('sms', 'permanent-failure', 100),
+        StatsRow('sms', 'delivered', 300),
+        StatsRow('email', 'delivered', 300),
+        StatsRow('letter', 'created', 300),
+    ], 0.25),
+    'only_counts_permanent_failure_as_failed': ([
+        StatsRow('sms', 'permanent-failure', 100),
+        StatsRow('sms', 'temporary-failure', 100),
+        StatsRow('sms', 'delivered', 300),
+    ], 0.2),
+    'below_threshold': ([
+        StatsRow('sms', 'permanent-failure', 5),
+        StatsRow('sms', 'delivered', 3),
+    ], 0),
+})
+def test_get_rate_of_permanent_failures_for_service(statistics, expected_result):
+    rate = get_rate_of_permanent_failures_for_service(statistics)
+    assert rate == expected_result
+
+
 def test_create_zeroed_stats_dicts():
     assert create_zeroed_stats_dicts() == {
         'sms': {'requested': 0, 'delivered': 0, 'failed': 0},