send users back to beginning of tour if they hit back at end

(previously it would have sent them to the choose template page)
if the user has added new templates or deleted the example one,
they're clearly competent enough to use the app so don't worry
(we wouldn't know what URL the tour starts on since the UUID of
the example template is random)

tests/app/main/views/test_send.py

@@ -6,13 +6,14 @@ import re
 from itertools import repeat
 from functools import partial
 from unittest.mock import patch
-from urllib.parse import urlparse
 
 import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
 
-from tests import validate_route_permission
+from app.main.views.send import get_check_messages_back_url
+
+from tests import validate_route_permission, template_json
 
 template_types = ['email', 'sms']
 
@@ -885,21 +886,59 @@ def test_check_messages_shows_over_max_row_error(
     )
 
 
-def test_check_messages_goes_to_select_template_if_no_upload_data(logged_in_client):
-    service_id = uuid.uuid4()
-
+def test_check_messages_redirects_if_no_upload_data(logged_in_client, mocker):
+    checker = mocker.patch('app.main.views.send.get_check_messages_back_url', return_value='foo')
     response = logged_in_client.get(url_for(
         'main.check_messages',
-        service_id=service_id,
-        template_type='sms',
-        upload_id=uuid.uuid4(),
+        service_id='0',
+        template_type='bar',
+        upload_id='baz'
     ))
 
-    # permanent redirect
+    checker.assert_called_once_with('0', 'bar')
     assert response.status_code == 301
-    assert response.location == url_for(
+    assert response.location == 'http://localhost/foo'
+
+
+@pytest.mark.parametrize('template_type', ['sms', 'email'])
+def test_get_check_messages_back_url_returns_to_correct_select_template(client, mocker, template_type):
+    mocker.patch('app.main.views.send.get_help_argument', return_value=False)
+
+    assert get_check_messages_back_url('1234', template_type) == url_for(
         'main.choose_template',
-        service_id=service_id,
-        template_type='sms',
-        _external=True
+        service_id='1234',
+        template_type=template_type
+    )
+
+
+def test_check_messages_back_from_help_goes_to_start_of_help(client, mocker):
+    mocker.patch('app.main.views.send.get_help_argument', return_value=True)
+    mocker.patch('app.service_api_client.get_service_templates', lambda service_id: {
+        'data': [template_json('000', '111', type_='sms')]
+    })
+    assert get_check_messages_back_url('000', 'sms') == url_for(
+        'main.send_test',
+        service_id='000',
+        template_id='111',
+        help='1'
+    )
+
+
+@pytest.mark.parametrize('templates', [
+    [],
+    [
+        template_json('000', '111', type_='sms'),
+        template_json('000', '222', type_='sms')
+    ]
+], ids=['no_templates', 'two_templates'])
+def test_check_messages_back_from_help_handles_unexpected_templates(client, mocker, templates):
+    mocker.patch('app.main.views.send.get_help_argument', return_value=True)
+    mocker.patch('app.service_api_client.get_service_templates', lambda service_id: {
+        'data': templates
+    })
+
+    assert get_check_messages_back_url('1234', 'sms') == url_for(
+        'main.choose_template',
+        service_id='1234',
+        template_type='sms'
     )