diff --git a/tests/app/celery/test_service_callback_tasks.py b/tests/app/celery/test_service_callback_tasks.py
index ff41a2eb5..5dd7f18ca 100644
--- a/tests/app/celery/test_service_callback_tasks.py
+++ b/tests/app/celery/test_service_callback_tasks.py
@@ -10,6 +10,7 @@ from app.celery.service_callback_tasks import (
     send_complaint_to_service,
     send_delivery_status_to_service,
 )
+from app.enums import CallbackType, NotificationStatus, NotificationType
 from app.utils import DATETIME_FORMAT
 from tests.app.db import (
     create_complaint,
@@ -20,7 +21,7 @@ from tests.app.db import (
 )
 
 
-@pytest.mark.parametrize("notification_type", ["email", "sms"])
+@pytest.mark.parametrize("notification_type", [NotificationType.EMAIL, NotificationType.SMS])
 def test_send_delivery_status_to_service_post_https_request_to_service_with_encrypted_data(
     notify_db_session, notification_type
 ):
@@ -32,7 +33,7 @@ def test_send_delivery_status_to_service_post_https_request_to_service_with_encr
         created_at=datestr,
         updated_at=datestr,
         sent_at=datestr,
-        status="sent",
+        status=NotificationStatus.SENT,
     )
     encrypted_status_update = _set_up_data_for_status_update(callback_api, notification)
     with requests_mock.Mocker() as request_mock:
@@ -102,7 +103,7 @@ def test_send_complaint_to_service_posts_https_request_to_service_with_encrypted
         ] == "Bearer {}".format(callback_api.bearer_token)
 
 
-@pytest.mark.parametrize("notification_type", ["email", "sms"])
+@pytest.mark.parametrize("notification_type", [NotificationType.EMAIL, NotificationType.SMS],)
 @pytest.mark.parametrize("status_code", [429, 500, 503])
 def test__send_data_to_service_callback_api_retries_if_request_returns_error_code_with_encrypted_data(
     notify_db_session, mocker, notification_type, status_code
@@ -114,7 +115,7 @@ def test__send_data_to_service_callback_api_retries_if_request_returns_error_cod
         created_at=datestr,
         updated_at=datestr,
         sent_at=datestr,
-        status="sent",
+        status=NotificationStatus.SENT,
     )
     encrypted_data = _set_up_data_for_status_update(callback_api, notification)
     mocked = mocker.patch(
@@ -130,7 +131,7 @@ def test__send_data_to_service_callback_api_retries_if_request_returns_error_cod
     assert mocked.call_args[1]["queue"] == "service-callbacks-retry"
 
 
-@pytest.mark.parametrize("notification_type", ["email", "sms"])
+@pytest.mark.parametrize("notification_type", [NotificationType.EMAIL, NotificationType.SMS],)
 def test__send_data_to_service_callback_api_does_not_retry_if_request_returns_404_with_encrypted_data(
     notify_db_session, mocker, notification_type
 ):
@@ -159,7 +160,7 @@ def test__send_data_to_service_callback_api_does_not_retry_if_request_returns_40
 def test_send_delivery_status_to_service_succeeds_if_sent_at_is_none(
     notify_db_session, mocker
 ):
-    callback_api, template = _set_up_test_data("email", "delivery_status")
+    callback_api, template = _set_up_test_data(NotificationType.EMAIL, CallbackType.DELIVERY_STATUS,)
     datestr = datetime(2017, 6, 20)
     notification = create_notification(
         template=template,
diff --git a/tests/app/celery/test_tasks.py b/tests/app/celery/test_tasks.py
index c615ee586..bda1837a3 100644
--- a/tests/app/celery/test_tasks.py
+++ b/tests/app/celery/test_tasks.py
@@ -194,7 +194,7 @@ def test_should_not_create_save_task_for_empty_file(sample_job, mocker):
         service_id=str(sample_job.service.id), job_id=str(sample_job.id)
     )
     job = jobs_dao.dao_get_job_by_id(sample_job.id)
-    assert job.job_status == "finished"
+    assert job.job_status == JobStatus.FINISHED
     assert tasks.save_sms.apply_async.called is False
 
 
@@ -420,13 +420,13 @@ def test_should_send_template_to_correct_sms_task_and_persist(
         persisted_notification.template_version
         == sample_template_with_placeholders.version
     )
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert persisted_notification.created_at <= datetime.utcnow()
     assert not persisted_notification.sent_at
     assert not persisted_notification.sent_by
     assert not persisted_notification.job_id
     assert persisted_notification.personalisation == {"name": "Jo"}
-    assert persisted_notification.notification_type == "sms"
+    assert persisted_notification.notification_type == NotificationType.SMS
     mocked_deliver_sms.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-sms-tasks"
     )
@@ -456,13 +456,13 @@ def test_should_save_sms_if_restricted_service_and_valid_number(
     assert persisted_notification.to == "1"
     assert persisted_notification.template_id == template.id
     assert persisted_notification.template_version == template.version
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert persisted_notification.created_at <= datetime.utcnow()
     assert not persisted_notification.sent_at
     assert not persisted_notification.sent_by
     assert not persisted_notification.job_id
     assert not persisted_notification.personalisation
-    assert persisted_notification.notification_type == "sms"
+    assert persisted_notification.notification_type == NotificationType.SMS
     provider_tasks.deliver_sms.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-sms-tasks"
     )
@@ -475,7 +475,7 @@ def test_save_email_should_save_default_email_reply_to_text_on_notification(
     create_reply_to_email(
         service=service, email_address="reply_to@digital.fake.gov", is_default=True
     )
-    template = create_template(service=service, template_type="email", subject="Hello")
+    template = create_template(service=service, template_type=TemplateType.EMAIL, subject="Hello",)
 
     notification = _notification_json(template, to="test@example.com")
     mocker.patch("app.celery.provider_tasks.deliver_email.apply_async")
@@ -536,7 +536,7 @@ def test_should_not_save_email_if_restricted_service_and_invalid_email_address(
 ):
     user = create_user()
     service = create_service(user=user, restricted=True)
-    template = create_template(service=service, template_type="email", subject="Hello")
+    template = create_template(service=service, template_type=TemplateType.EMAIL, subject="Hello",)
     notification = _notification_json(template, to="test@example.com")
 
     notification_id = uuid.uuid4()
@@ -551,7 +551,7 @@ def test_should_not_save_email_if_restricted_service_and_invalid_email_address(
 
 def test_should_save_sms_template_to_and_persist_with_job_id(sample_job, mocker):
     notification = _notification_json(
-        sample_job.template, to="+447234123123", job_id=sample_job.id, row_number=2
+        sample_job.template, to="+447234123123", job_id=sample_job.id, row_number=2,
     )
     mocker.patch("app.celery.provider_tasks.deliver_sms.apply_async")
 
@@ -566,14 +566,14 @@ def test_should_save_sms_template_to_and_persist_with_job_id(sample_job, mocker)
     assert persisted_notification.to == "1"
     assert persisted_notification.job_id == sample_job.id
     assert persisted_notification.template_id == sample_job.template.id
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert not persisted_notification.sent_at
     assert persisted_notification.created_at >= now
     assert not persisted_notification.sent_by
     assert persisted_notification.job_row_number == 2
     assert persisted_notification.api_key_id is None
     assert persisted_notification.key_type == KeyType.NORMAL
-    assert persisted_notification.notification_type == "sms"
+    assert persisted_notification.notification_type == NotificationType.SMS
 
     provider_tasks.deliver_sms.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-sms-tasks"
@@ -638,13 +638,13 @@ def test_should_use_email_template_and_persist(
     )
     assert persisted_notification.created_at >= now
     assert not persisted_notification.sent_at
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert not persisted_notification.sent_by
     assert persisted_notification.job_row_number == 1
     assert persisted_notification.personalisation == {"name": "Jo"}
     assert persisted_notification.api_key_id is None
     assert persisted_notification.key_type == KeyType.NORMAL
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
 
     provider_tasks.deliver_email.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-email-tasks"
@@ -680,9 +680,9 @@ def test_save_email_should_use_template_version_from_job_not_latest(
     assert persisted_notification.template_version == version_on_notification
     assert persisted_notification.created_at >= now
     assert not persisted_notification.sent_at
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert not persisted_notification.sent_by
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
     provider_tasks.deliver_email.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-email-tasks"
     )
@@ -708,12 +708,12 @@ def test_should_use_email_template_subject_placeholders(
     assert (
         persisted_notification.template_id == sample_email_template_with_placeholders.id
     )
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert persisted_notification.created_at >= now
     assert not persisted_notification.sent_by
     assert persisted_notification.personalisation == {"name": "Jo"}
     assert not persisted_notification.reference
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
     provider_tasks.deliver_email.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-email-tasks"
     )
@@ -726,11 +726,11 @@ def test_save_email_uses_the_reply_to_text_when_provided(sample_email_template,
     service = sample_email_template.service
     notification_id = uuid.uuid4()
     service_email_reply_to_dao.add_reply_to_email_address_for_service(
-        service.id, "default@example.com", True
+        service.id, "default@example.com", True,
     )
     other_email_reply_to = (
         service_email_reply_to_dao.add_reply_to_email_address_for_service(
-            service.id, "other@example.com", False
+            service.id, "other@example.com", False,
         )
     )
 
@@ -741,7 +741,7 @@ def test_save_email_uses_the_reply_to_text_when_provided(sample_email_template,
         sender_id=other_email_reply_to.id,
     )
     persisted_notification = Notification.query.one()
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
     assert persisted_notification.reply_to_text == "other@example.com"
 
 
@@ -754,7 +754,7 @@ def test_save_email_uses_the_default_reply_to_text_if_sender_id_is_none(
     service = sample_email_template.service
     notification_id = uuid.uuid4()
     service_email_reply_to_dao.add_reply_to_email_address_for_service(
-        service.id, "default@example.com", True
+        service.id, "default@example.com", True,
     )
 
     save_email(
@@ -764,7 +764,7 @@ def test_save_email_uses_the_default_reply_to_text_if_sender_id_is_none(
         sender_id=None,
     )
     persisted_notification = Notification.query.one()
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
     assert persisted_notification.reply_to_text == "default@example.com"
 
 
@@ -787,11 +787,11 @@ def test_should_use_email_template_and_persist_without_personalisation(
     assert persisted_notification.template_id == sample_email_template.id
     assert persisted_notification.created_at >= now
     assert not persisted_notification.sent_at
-    assert persisted_notification.status == "created"
+    assert persisted_notification.status == NotificationStatus.CREATED
     assert not persisted_notification.sent_by
     assert not persisted_notification.personalisation
     assert not persisted_notification.reference
-    assert persisted_notification.notification_type == "email"
+    assert persisted_notification.notification_type == NotificationType.EMAIL
     provider_tasks.deliver_email.apply_async.assert_called_once_with(
         [str(persisted_notification.id)], queue="send-email-tasks"
     )
@@ -925,7 +925,7 @@ def test_save_sms_uses_non_default_sms_sender_reply_to_text_if_provided(
     service = create_service_with_defined_sms_sender(sms_sender_value="2028675309")
     template = create_template(service=service)
     new_sender = service_sms_sender_dao.dao_add_sms_sender_for_service(
-        service.id, "new-sender", False
+        service.id, "new-sender", False,
     )
 
     notification = _notification_json(template, to="202-867-5301")
@@ -952,7 +952,7 @@ def test_should_cancel_job_if_service_is_inactive(sample_service, sample_job, mo
     process_job(sample_job.id)
 
     job = jobs_dao.dao_get_job_by_id(sample_job.id)
-    assert job.job_status == "cancelled"
+    assert job.job_status == JobStatus.CANCELLED
     s3.get_job_from_s3.assert_not_called()
     tasks.process_row.assert_not_called()
 
@@ -1377,7 +1377,7 @@ def test_process_incomplete_jobs_sets_status_to_in_progress_and_resets_processin
 
 
 @freeze_time("2020-03-25 14:30")
-@pytest.mark.parametrize("notification_type", ["sms", "email"])
+@pytest.mark.parametrize("notification_type", [NotificationType.SMS, NotificationType.EMAIL],)
 def test_save_api_email_or_sms(mocker, sample_service, notification_type):
     template = (
         create_template(sample_service)
@@ -1427,7 +1427,7 @@ def test_save_api_email_or_sms(mocker, sample_service, notification_type):
 
 
 @freeze_time("2020-03-25 14:30")
-@pytest.mark.parametrize("notification_type", ["sms", "email"])
+@pytest.mark.parametrize("notification_type", [NotificationType.SMS, NotificationType.EMAIL])
 def test_save_api_email_dont_retry_if_notification_already_exists(
     sample_service, mocker, notification_type
 ):
@@ -1492,13 +1492,13 @@ def test_save_api_email_dont_retry_if_notification_already_exists(
             save_email,
             "app.celery.provider_tasks.deliver_email.apply_async",
             "test@example.com",
-            {"template_type": "email", "subject": "Hello"},
+            {"template_type": TemplateType.EMAIL, "subject": "Hello"},
         ),
         (
             save_sms,
             "app.celery.provider_tasks.deliver_sms.apply_async",
             "202-867-5309",
-            {"template_type": "sms"},
+            {"template_type": TemplateType.SMS},
         ),
     ),
 )
@@ -1549,8 +1549,8 @@ def test_save_tasks_use_cached_service_and_template(
 @pytest.mark.parametrize(
     "notification_type, task_function, expected_queue, recipient",
     (
-        ("sms", save_api_sms, QueueNames.SEND_SMS, "+447700900855"),
-        ("email", save_api_email, QueueNames.SEND_EMAIL, "jane.citizen@example.com"),
+        (NotificationType.SMS, save_api_sms, QueueNames.SEND_SMS, "+447700900855",),
+        (NotificationType.EMAIL, save_api_email, QueueNames.SEND_EMAIL, "jane.citizen@example.com",),
     ),
 )
 def test_save_api_tasks_use_cache(
diff --git a/tests/app/dao/test_fact_billing_dao.py b/tests/app/dao/test_fact_billing_dao.py
index 90bfb6d69..41a3dd485 100644
--- a/tests/app/dao/test_fact_billing_dao.py
+++ b/tests/app/dao/test_fact_billing_dao.py
@@ -21,8 +21,8 @@ from app.dao.fact_billing_dao import (
     query_organization_sms_usage_for_year,
 )
 from app.dao.organization_dao import dao_add_service_to_organization
-from app.enums import NotificationStatus
-from app.models import FactBilling
+from app.enums import NotificationStatus, NotificationType, TemplateType
+from app.models import FactBilling, Notification
 from tests.app.db import (
     create_annual_billing,
     create_ft_billing,
@@ -39,8 +39,8 @@ from tests.app.db import (
 
 def set_up_yearly_data():
     service = create_service()
-    sms_template = create_template(service=service, template_type="sms")
-    email_template = create_template(service=service, template_type="email")
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
 
     # use different rates for adjacent financial years to make sure the query
     # doesn't accidentally bleed over into them
@@ -68,7 +68,7 @@ def set_up_yearly_data():
 
 def set_up_yearly_data_variable_rates():
     service = create_service()
-    sms_template = create_template(service=service, template_type="sms")
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
 
     create_ft_billing(local_date="2018-05-16", template=sms_template, rate=0.162)
     create_ft_billing(
@@ -93,9 +93,9 @@ def test_fetch_billing_data_for_today_includes_data_with_the_right_key_type(
     notify_db_session,
 ):
     service = create_service()
-    template = create_template(service=service, template_type="email")
+    template = create_template(service=service, template_type=TemplateType.EMAIL)
     for key_type in ["normal", "test", "team"]:
-        create_notification(template=template, status="delivered", key_type=key_type)
+        create_notification(template=template, status=NotificationStatus.DELIVERED, key_type=key_type,)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -103,13 +103,13 @@ def test_fetch_billing_data_for_today_includes_data_with_the_right_key_type(
     assert results[0].notifications_sent == 2
 
 
-@pytest.mark.parametrize("notification_type", ["email", "sms"])
+@pytest.mark.parametrize("notification_type", [NotificationType.EMAIL, NotificationType.SMS])
 def test_fetch_billing_data_for_day_only_calls_query_for_permission_type(
     notify_db_session, notification_type
 ):
     service = create_service(service_permissions=[notification_type])
-    email_template = create_template(service=service, template_type="email")
-    sms_template = create_template(service=service, template_type="sms")
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
     create_notification(template=email_template, status="delivered")
     create_notification(template=sms_template, status="delivered")
     today = datetime.utcnow()
@@ -119,18 +119,18 @@ def test_fetch_billing_data_for_day_only_calls_query_for_permission_type(
     assert len(results) == 1
 
 
-@pytest.mark.parametrize("notification_type", ["email", "sms"])
+@pytest.mark.parametrize("notification_type", [NotificationType.EMAIL, NotificationType.SMS],)
 def test_fetch_billing_data_for_day_only_calls_query_for_all_channels(
     notify_db_session, notification_type
 ):
     service = create_service(service_permissions=[notification_type])
-    email_template = create_template(service=service, template_type="email")
-    sms_template = create_template(service=service, template_type="sms")
-    create_notification(template=email_template, status="delivered")
-    create_notification(template=sms_template, status="delivered")
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    create_notification(template=email_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(
-        process_day=today.date(), check_permissions=False
+        process_day=today.date(), check_permissions=False,
     )
     assert len(results) == 2
 
@@ -141,21 +141,21 @@ def test_fetch_billing_data_for_today_includes_data_with_the_right_date(
 ):
     process_day = datetime(2018, 4, 1, 13, 30, 0)
     service = create_service()
-    template = create_template(service=service, template_type="email")
-    create_notification(template=template, status="delivered", created_at=process_day)
+    template = create_template(service=service, template_type=TemplateType.EMAIL)
+    create_notification(template=template, status=NotificationStatus.DELIVERED, created_at=process_day,)
     create_notification(
         template=template,
-        status="delivered",
+        status=NotificationStatus.DELIVERED,
         created_at=datetime(2018, 4, 1, 4, 23, 23),
     )
 
     create_notification(
         template=template,
-        status="delivered",
+        status=NotificationStatus.DELIVERED,
         created_at=datetime(2018, 4, 1, 0, 23, 23),
     )
     create_notification(
-        template=template, status="sending", created_at=process_day + timedelta(days=1)
+        template=template, status=NotificationStatus.SENDING, created_at=process_day + timedelta(days=1,)
     )
 
     day_under_test = process_day
@@ -168,10 +168,10 @@ def test_fetch_billing_data_for_day_is_grouped_by_template_and_notification_type
     notify_db_session,
 ):
     service = create_service()
-    email_template = create_template(service=service, template_type="email")
-    sms_template = create_template(service=service, template_type="sms")
-    create_notification(template=email_template, status="delivered")
-    create_notification(template=sms_template, status="delivered")
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    create_notification(template=email_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -185,8 +185,8 @@ def test_fetch_billing_data_for_day_is_grouped_by_service(notify_db_session):
     service_2 = create_service(service_name="Service 2")
     email_template = create_template(service=service_1)
     sms_template = create_template(service=service_2)
-    create_notification(template=email_template, status="delivered")
-    create_notification(template=sms_template, status="delivered")
+    create_notification(template=email_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -198,8 +198,8 @@ def test_fetch_billing_data_for_day_is_grouped_by_service(notify_db_session):
 def test_fetch_billing_data_for_day_is_grouped_by_provider(notify_db_session):
     service = create_service()
     template = create_template(service=service)
-    create_notification(template=template, status="delivered", sent_by="sns")
-    create_notification(template=template, status="delivered", sent_by="sns")
+    create_notification(template=template, status=NotificationStatus.DELIVERED, sent_by="sns",)
+    create_notification(template=template, status=NotificationStatus.DELIVERED, sent_by="sns",)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -211,8 +211,8 @@ def test_fetch_billing_data_for_day_is_grouped_by_provider(notify_db_session):
 def test_fetch_billing_data_for_day_is_grouped_by_rate_mulitplier(notify_db_session):
     service = create_service()
     template = create_template(service=service)
-    create_notification(template=template, status="delivered", rate_multiplier=1)
-    create_notification(template=template, status="delivered", rate_multiplier=2)
+    create_notification(template=template, status=NotificationStatus.DELIVERED, rate_multiplier=1,)
+    create_notification(template=template, status=NotificationStatus.DELIVERED, rate_multiplier=2,)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -224,8 +224,8 @@ def test_fetch_billing_data_for_day_is_grouped_by_rate_mulitplier(notify_db_sess
 def test_fetch_billing_data_for_day_is_grouped_by_international(notify_db_session):
     service = create_service()
     sms_template = create_template(service=service)
-    create_notification(template=sms_template, status="delivered", international=True)
-    create_notification(template=sms_template, status="delivered", international=False)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED, international=True,)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED, international=False,)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -235,13 +235,13 @@ def test_fetch_billing_data_for_day_is_grouped_by_international(notify_db_sessio
 
 def test_fetch_billing_data_for_day_is_grouped_by_notification_type(notify_db_session):
     service = create_service()
-    sms_template = create_template(service=service, template_type="sms")
-    email_template = create_template(service=service, template_type="email")
-    create_notification(template=sms_template, status="delivered")
-    create_notification(template=sms_template, status="delivered")
-    create_notification(template=sms_template, status="delivered")
-    create_notification(template=email_template, status="delivered")
-    create_notification(template=email_template, status="delivered")
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=sms_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=email_template, status=NotificationStatus.DELIVERED)
+    create_notification(template=email_template, status=NotificationStatus.DELIVERED)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(today.date())
@@ -259,26 +259,26 @@ def test_fetch_billing_data_for_day_returns_empty_list(notify_db_session):
 def test_fetch_billing_data_for_day_uses_correct_table(notify_db_session):
     service = create_service()
     create_service_data_retention(
-        service, notification_type="email", days_of_retention=3
+        service, notification_type=NotificationType.EMAIL, days_of_retention=3
     )
-    sms_template = create_template(service=service, template_type="sms")
-    email_template = create_template(service=service, template_type="email")
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
 
     five_days_ago = datetime.utcnow() - timedelta(days=5)
     create_notification(
-        template=sms_template, status="delivered", created_at=five_days_ago
+        template=sms_template, status=NotificationStatus.DELIVERED, created_at=five_days_ago,
     )
     create_notification_history(
-        template=email_template, status="delivered", created_at=five_days_ago
+        template=email_template, status=NotificationStatus.DELIVERED, created_at=five_days_ago,
     )
 
     results = fetch_billing_data_for_day(
         process_day=five_days_ago.date(), service_id=service.id
     )
     assert len(results) == 2
-    assert results[0].notification_type == "sms"
+    assert results[0].notification_type == NotificationType.SMS
     assert results[0].notifications_sent == 1
-    assert results[1].notification_type == "email"
+    assert results[1].notification_type == NotificationType.EMAIL
     assert results[1].notifications_sent == 1
 
 
@@ -287,8 +287,8 @@ def test_fetch_billing_data_for_day_returns_list_for_given_service(notify_db_ses
     service_2 = create_service(service_name="Service 2")
     template = create_template(service=service)
     template_2 = create_template(service=service_2)
-    create_notification(template=template, status="delivered")
-    create_notification(template=template_2, status="delivered")
+    create_notification(template=template, status=NotificationStatus.DELIVERED)
+    create_notification(template=template_2, status=NotificationStatus.DELIVERED)
 
     today = datetime.utcnow()
     results = fetch_billing_data_for_day(
@@ -300,8 +300,8 @@ def test_fetch_billing_data_for_day_returns_list_for_given_service(notify_db_ses
 
 def test_fetch_billing_data_for_day_bills_correctly_for_status(notify_db_session):
     service = create_service()
-    sms_template = create_template(service=service, template_type="sms")
-    email_template = create_template(service=service, template_type="email")
+    sms_template = create_template(service=service, template_type=TemplateType.SMS)
+    email_template = create_template(service=service, template_type=TemplateType.EMAIL)
     for status in NotificationStatus:
         create_notification(template=sms_template, status=status)
         create_notification(template=email_template, status=status)
@@ -310,17 +310,17 @@ def test_fetch_billing_data_for_day_bills_correctly_for_status(notify_db_session
         process_day=today.date(), service_id=service.id
     )
 
-    sms_results = [x for x in results if x.notification_type == "sms"]
-    email_results = [x for x in results if x.notification_type == "email"]
+    sms_results = [x for x in results if x.notification_type == NotificationType.SMS]
+    email_results = [x for x in results if x.notification_type == NotificationType.EMAIL]
     # we expect as many rows as we check for notification types
     assert 6 == sms_results[0].notifications_sent
     assert 4 == email_results[0].notifications_sent
 
 
 def test_get_rates_for_billing(notify_db_session):
-    create_rate(start_date=datetime.utcnow(), value=12, notification_type="email")
-    create_rate(start_date=datetime.utcnow(), value=22, notification_type="sms")
-    create_rate(start_date=datetime.utcnow(), value=33, notification_type="email")
+    create_rate(start_date=datetime.utcnow(), value=12, notification_type=NotificationType.EMAIL)
+    create_rate(start_date=datetime.utcnow(), value=22, notification_type=NotificationType.SMS)
+    create_rate(start_date=datetime.utcnow(), value=33, notification_type=NotificationType.EMAIL)
     rates = get_rates_for_billing()
 
     assert len(rates) == 3
@@ -329,17 +329,17 @@ def test_get_rates_for_billing(notify_db_session):
 @freeze_time("2017-06-01 12:00")
 def test_get_rate(notify_db_session):
     create_rate(
-        start_date=datetime(2017, 5, 30, 23, 0), value=1.2, notification_type="email"
+        start_date=datetime(2017, 5, 30, 23, 0), value=1.2, notification_type=NotificationType.EMAIL,
     )
     create_rate(
-        start_date=datetime(2017, 5, 30, 23, 0), value=2.2, notification_type="sms"
+        start_date=datetime(2017, 5, 30, 23, 0), value=2.2, notification_type=NotificationType.SMS,
     )
     create_rate(
-        start_date=datetime(2017, 5, 30, 23, 0), value=3.3, notification_type="email"
+        start_date=datetime(2017, 5, 30, 23, 0), value=3.3, notification_type=NotificationType.EMAIL,
     )
 
     rates = get_rates_for_billing()
-    rate = get_rate(rates, notification_type="sms", date=date(2017, 6, 1))
+    rate = get_rate(rates, notification_type=NotificationType.SMS, date=date(2017, 6, 1))
 
     assert rate == 2.2
 
@@ -351,14 +351,14 @@ def test_get_rate_chooses_right_rate_depending_on_date(
     notify_db_session, date, expected_rate
 ):
     create_rate(
-        start_date=datetime(2016, 1, 1, 0, 0), value=1.2, notification_type="sms"
+        start_date=datetime(2016, 1, 1, 0, 0), value=1.2, notification_type=NotificationType.SMS,
     )
     create_rate(
-        start_date=datetime(2018, 9, 30, 23, 0), value=2.2, notification_type="sms"
+        start_date=datetime(2018, 9, 30, 23, 0), value=2.2, notification_type=NotificationType.SMS,
     )
 
     rates = get_rates_for_billing()
-    rate = get_rate(rates, "sms", date)
+    rate = get_rate(rates, NotificationType.SMS, date)
     assert rate == expected_rate
 
 
@@ -373,7 +373,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     print(f"RESULTS {results}")
 
     assert str(results[0].month) == "2016-01-01"
-    assert results[0].notification_type == "email"
+    assert results[0].notification_type == NotificationType.EMAIL
     assert results[0].notifications_sent == 2
     assert results[0].chargeable_units == 0
     assert results[0].rate == Decimal("0")
@@ -382,7 +382,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
     assert results[0].charged_units == 0
 
     assert str(results[1].month) == "2016-01-01"
-    assert results[1].notification_type == "sms"
+    assert results[1].notification_type == NotificationType.SMS
     assert results[1].notifications_sent == 2
     assert results[1].chargeable_units == 2
     assert results[1].rate == Decimal("0.162")
@@ -397,7 +397,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
 def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     service = set_up_yearly_data_variable_rates()
     create_annual_billing(
-        service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018
+        service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018,
     )
     results = fetch_monthly_billing_for_year(service.id, 2018)
 
@@ -405,7 +405,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     assert len(results) == 2
 
     assert str(results[0].month) == "2018-05-01"
-    assert results[0].notification_type == "sms"
+    assert results[0].notification_type == NotificationType.SMS
     assert results[0].notifications_sent == 1
     assert results[0].chargeable_units == 4
     assert results[0].rate == Decimal("0.015")
@@ -415,7 +415,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
     assert results[0].charged_units == 3
 
     assert str(results[1].month) == "2018-05-01"
-    assert results[1].notification_type == "sms"
+    assert results[1].notification_type == NotificationType.SMS
     assert results[1].notifications_sent == 2
     assert results[1].chargeable_units == 5
     assert results[1].rate == Decimal("0.162")
@@ -428,12 +428,12 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
 @freeze_time("2018-08-01 13:30:00")
 def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
     service = create_service()
-    template = create_template(service=service, template_type="sms")
+    template = create_template(service=service, template_type=TemplateType.SMS)
 
     create_rate(
         start_date=datetime.utcnow() - timedelta(days=1),
         value=0.158,
-        notification_type="sms",
+        notification_type=NotificationType.SMS,
     )
     create_annual_billing(
         service_id=service.id, free_sms_fragment_limit=1000, financial_year_start=2018
@@ -442,7 +442,7 @@ def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
     for i in range(1, 32):
         create_ft_billing(local_date="2018-07-{}".format(i), template=template)
 
-    create_notification(template=template, status="delivered")
+    create_notification(template=template, status=NotificationStatus.DELIVERED)
 
     assert db.session.query(FactBilling.local_date).count() == 31
     results = fetch_monthly_billing_for_year(service_id=service.id, year=2018)
@@ -459,7 +459,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     results = fetch_billing_totals_for_year(service_id=service.id, year=2016)
 
     assert len(results) == 2
-    assert results[0].notification_type == "email"
+    assert results[0].notification_type == NotificationType.EMAIL
     assert results[0].notifications_sent == 4
     assert results[0].chargeable_units == 0
     assert results[0].rate == Decimal("0")
@@ -467,7 +467,7 @@ def test_fetch_billing_totals_for_year(notify_db_session):
     assert results[0].free_allowance_used == 0
     assert results[0].charged_units == 0
 
-    assert results[1].notification_type == "sms"
+    assert results[1].notification_type == NotificationType.SMS
     assert results[1].notifications_sent == 4
     assert results[1].chargeable_units == 4
     assert results[1].rate == Decimal("0.162")
@@ -488,7 +488,7 @@ def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_ses
     result = next(
         result
         for result in fetch_billing_totals_for_year(service_id=service.id, year=2016)
-        if result.notification_type == "sms"
+        if result.notification_type == NotificationType.SMS
     )
 
     assert result.chargeable_units == 4
@@ -501,13 +501,13 @@ def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_ses
 def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     service = set_up_yearly_data_variable_rates()
     create_annual_billing(
-        service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018
+        service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018,
     )
     results = fetch_billing_totals_for_year(service_id=service.id, year=2018)
 
     assert len(results) == 2
 
-    assert results[0].notification_type == "sms"
+    assert results[0].notification_type == NotificationType.SMS
     assert results[0].notifications_sent == 1
     assert results[0].chargeable_units == 4
     assert results[0].rate == Decimal("0.015")
@@ -516,7 +516,7 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
     assert results[0].free_allowance_used == 1
     assert results[0].charged_units == 3
 
-    assert results[1].notification_type == "sms"
+    assert results[1].notification_type == NotificationType.SMS
     assert results[1].notifications_sent == 2
     assert results[1].chargeable_units == 5
     assert results[1].rate == Decimal("0.162")
@@ -529,9 +529,9 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
 def test_delete_billing_data(notify_db_session):
     service_1 = create_service(service_name="1")
     service_2 = create_service(service_name="2")
-    sms_template = create_template(service_1, "sms")
-    email_template = create_template(service_1, "email")
-    other_service_template = create_template(service_2, "sms")
+    sms_template = create_template(service_1, TemplateType.SMS)
+    email_template = create_template(service_1, TemplateType.EMAIL)
+    other_service_template = create_template(service_2, TemplateType.SMS)
 
     existing_rows_to_delete = [  # noqa
         create_ft_billing("2018-01-01", sms_template, billable_unit=1),
@@ -558,13 +558,13 @@ def test_fetch_sms_free_allowance_remainder_until_date_with_two_services(
     org = create_organization(name="Org for {}".format(service.name))
     dao_add_service_to_organization(service=service, organization_id=org.id)
     create_annual_billing(
-        service_id=service.id, free_sms_fragment_limit=10, financial_year_start=2016
+        service_id=service.id, free_sms_fragment_limit=10, financial_year_start=2016,
     )
     create_ft_billing(
-        template=template, local_date=datetime(2016, 4, 20), billable_unit=2, rate=0.11
+        template=template, local_date=datetime(2016, 4, 20), billable_unit=2, rate=0.11,
     )
     create_ft_billing(
-        template=template, local_date=datetime(2016, 5, 20), billable_unit=3, rate=0.11
+        template=template, local_date=datetime(2016, 5, 20), billable_unit=3, rate=0.11,
     )
 
     service_2 = create_service(service_name="used free allowance")
@@ -693,7 +693,7 @@ def test_fetch_sms_billing_for_all_services_with_remainder(notify_db_session):
     )
 
     service_4 = create_service(service_name="d - email only")
-    email_template = create_template(service=service_4, template_type="email")
+    email_template = create_template(service=service_4, template_type=TemplateType.EMAIL)
     org_4 = create_organization(name="Org for {}".format(service_4.name))
     dao_add_service_to_organization(service=service_4, organization_id=org_4.id)
     create_annual_billing(
@@ -827,13 +827,13 @@ def test_fetch_usage_year_for_organization(notify_db_session):
         financial_year_start=2019,
     )
     dao_add_service_to_organization(
-        service=service_with_emails_for_org, organization_id=fixtures["org_1"].id
+        service=service_with_emails_for_org, organization_id=fixtures["org_1"].id,
     )
     template = create_template(
-        service=service_with_emails_for_org, template_type="email"
+        service=service_with_emails_for_org, template_type=TemplateType.EMAIL,
     )
     create_ft_billing(
-        local_date=datetime(2019, 5, 1), template=template, notifications_sent=1100
+        local_date=datetime(2019, 5, 1), template=template, notifications_sent=1100,
     )
     results = fetch_usage_year_for_organization(fixtures["org_1"].id, 2019)
 
@@ -877,7 +877,7 @@ def test_fetch_usage_year_for_organization_populates_ft_billing_for_today(
     create_rate(
         start_date=datetime.utcnow() - timedelta(days=1),
         value=0.65,
-        notification_type="sms",
+        notification_type=NotificationType.SMS,
     )
     new_org = create_organization(name="New organization")
     service = create_service()
@@ -892,7 +892,7 @@ def test_fetch_usage_year_for_organization_populates_ft_billing_for_today(
 
     assert FactBilling.query.count() == 0
 
-    create_notification(template=template, status="delivered")
+    create_notification(template=template, status=NotificationStatus.DELIVERED)
 
     results = fetch_usage_year_for_organization(
         organization_id=new_org.id, year=current_year
@@ -1039,8 +1039,8 @@ def test_fetch_usage_year_for_organization_only_returns_data_for_live_services(
     live_service = create_service(restricted=False)
     sms_template = create_template(service=live_service)
     trial_service = create_service(restricted=True, service_name="trial_service")
-    email_template = create_template(service=trial_service, template_type="email")
-    trial_sms_template = create_template(service=trial_service, template_type="sms")
+    email_template = create_template(service=trial_service, template_type=TemplateType.EMAIL)
+    trial_sms_template = create_template(service=trial_service, template_type=TemplateType.SMS)
     dao_add_service_to_organization(service=live_service, organization_id=org.id)
     dao_add_service_to_organization(service=trial_service, organization_id=org.id)
     create_ft_billing(