New test for notification.cost() method

Added a test that asking for a nonexistent provider_rate blows
everything up.

Also updated existing test to use a weirder number.

tests/app/test_model.py

@@ -1,9 +1,9 @@
 import pytest
 from datetime import datetime
 
+from sqlalchemy.orm.exc import NoResultFound
 from tests.app.conftest import sample_notification, sample_provider_rate
 from app.models import (
-    Notification,
     ServiceWhitelist,
     MOBILE_TYPE, EMAIL_TYPE)
 
@@ -39,7 +39,7 @@ def test_should_not_build_service_whitelist_from_invalid_contact(recipient_type,
 
 @pytest.mark.parametrize('provider, billable_units, expected_cost', [
     ('mmg', 1, 3.5),
-    ('firetext', 2, 5),
+    ('firetext', 2, 0.025),
     ('ses', 0, 0)
 ])
 def test_calculate_cost_from_notification_billable_units(
@@ -47,7 +47,7 @@ def test_calculate_cost_from_notification_billable_units(
 ):
     provider_rates = [
         ('mmg', datetime(2016, 7, 1), 1.5),
-        ('firetext', datetime(2016, 7, 1), 2.5),
+        ('firetext', datetime(2016, 7, 1), 0.0125),
         ('mmg', datetime.utcnow(), 3.5),
     ]
     for provider_identifier, valid_from, rate in provider_rates:
@@ -61,3 +61,11 @@ def test_calculate_cost_from_notification_billable_units(
 
     notification = sample_notification(notify_db, notify_db_session, billable_units=billable_units, sent_by=provider)
     assert notification.cost() == expected_cost
+
+
+def test_billable_units_without_provider_rates_entry_raises_exception(
+        notify_db, notify_db_session, sample_provider_rate
+):
+    notification = sample_notification(notify_db, notify_db_session, sent_by='not_a_provider')
+    with pytest.raises(NoResultFound):
+        notification.cost()