Sprinkle letter throughout the app

Let users create/edit/delete letter templates.

Let them upload a CSV file or send a test against a letter template.

Big assumption at the moment is that addresses only have one line, and
therefore one column in the CSV file.

tests/app/main/views/test_letters.py

@@ -1,34 +1,51 @@
 import pytest
 from flask import url_for
+from functools import partial
 
 from tests import service_json
 
+letters_urls = [
+    partial(url_for, 'main.choose_template', template_type='letter'),
+    partial(url_for, 'main.add_service_template', template_type='letter'),
+]
 
+
+@pytest.mark.parametrize('url', letters_urls)
 @pytest.mark.parametrize('can_send_letters, response_code', [
     (True, 200),
     (False, 403)
 ])
-def test_letters_access_restricted(logged_in_client, mocker, can_send_letters, response_code):
+def test_letters_access_restricted(
+    logged_in_client,
+    mocker,
+    can_send_letters,
+    response_code,
+    mock_get_service_templates,
+    url
+):
     service = service_json(can_send_letters=can_send_letters)
     mocker.patch('app.service_api_client.get_service', return_value={"data": service})
 
-    response = logged_in_client.get(url_for('main.letters', service_id=service['id']))
+    response = logged_in_client.get(url(service_id=service['id']))
 
     assert response.status_code == response_code
 
 
+@pytest.mark.parametrize('url', letters_urls)
 def test_letters_lets_in_without_permission(
     client,
     mocker,
     mock_login,
     mock_has_permissions,
     api_user_active,
+    mock_get_service_templates,
+    url
 ):
     service = service_json(can_send_letters=True)
     mocker.patch('app.service_api_client.get_service', return_value={"data": service})
 
     client.login(api_user_active)
-    response = client.get(url_for('main.letters', service_id=service['id']))
+    response = client.get(url(service_id=service['id']))
 
     assert api_user_active.permissions == {}
     assert response.status_code == 200