Always go back to previous page from notification

When looking at a notification you can either be coming from the page
of all notifications, or from a job. Currently the back link always
takes you to the page of all notifications.

This commit makes it a bit more sophisticated so if you’ve come from
looking at a job, you go back to the job.

tests/app/main/views/test_jobs.py

@@ -5,6 +5,7 @@ from flask import url_for
 from freezegun import freeze_time
 
 from app.main.views.jobs import get_time_left
+from tests import sample_uuid
 from tests.conftest import (
     SERVICE_ONE_ID,
     active_caseworking_user,
@@ -218,6 +219,19 @@ def test_should_show_page_for_one_job(
     )
     assert csv_link.text == 'Download this report'
     assert page.find('span', {'id': 'time-left'}).text == 'Data available for 7 days'
+
+    assert normalize_spaces(page.select_one('tbody tr').text) == normalize_spaces(
+        '07123456789 '
+        'template content '
+        'Delivered 1 January at 11:10am'
+    )
+    assert page.select_one('tbody tr a')['href'] == url_for(
+        'main.view_notification',
+        service_id=SERVICE_ONE_ID,
+        notification_id=sample_uuid(),
+        from_job=fake_uuid,
+    )
+
     mock_get_notifications.assert_called_with(
         SERVICE_ONE_ID,
         fake_uuid,

tests/app/main/views/test_notifications.py

@@ -115,6 +115,46 @@ def test_notification_status_page_respects_redaction(
     )
 
 
+@pytest.mark.parametrize('extra_args, expected_back_link', [
+    (
+        {},
+        partial(url_for, 'main.view_notifications', message_type='sms'),
+    ),
+    (
+        {'from_job': 'job_id'},
+        partial(url_for, 'main.view_job', job_id='job_id'),
+    ),
+    (
+        {'help': '0'},
+        None,
+    ),
+    (
+        {'help': '0', 'from_job': 'job_id'},
+        None,
+    ),
+])
+def test_notification_status_shows_expected_back_link(
+    client_request,
+    mocker,
+    mock_get_notification,
+    fake_uuid,
+    extra_args,
+    expected_back_link,
+):
+    page = client_request.get(
+        'main.view_notification',
+        service_id=SERVICE_ONE_ID,
+        notification_id=fake_uuid,
+        **extra_args
+    )
+    back_link = page.select_one('.govuk-back-link')
+
+    if expected_back_link:
+        assert back_link['href'] == expected_back_link(service_id=SERVICE_ONE_ID)
+    else:
+        assert back_link is None
+
+
 @freeze_time("2012-01-01 01:01")
 def test_notification_page_doesnt_link_to_template_in_tour(
     client_request,