Preview content as hint for broadcast templates

Broadcast services only have broadcast templates. But we show the
template type under the name of the template. This is redundant. It
would be better to preview the content of the template instead.

This then makes the templates page consistent with the dashboard.

Depends on:
- [ ] https://github.com/alphagov/notifications-api/pull/2996

tests/app/main/views/test_templates.py

@@ -199,6 +199,75 @@ def test_should_show_page_for_choosing_a_template(
     mock_get_template_folders.assert_called_once_with(SERVICE_ONE_ID)
 
 
+def test_should_show_page_of_broadcast_templates(
+    mocker,
+    client_request,
+    service_one,
+    fake_uuid,
+    mock_get_template_folders,
+):
+    service_one['permissions'] += ['broadcast']
+    mocker.patch(
+        'app.service_api_client.get_service_templates',
+        return_value={'data': [
+            template_json(
+                SERVICE_ONE_ID,
+                fake_uuid,
+                type_='broadcast',
+                name='A',
+                content='a' * 40,
+            ),
+            template_json(
+                SERVICE_ONE_ID,
+                fake_uuid,
+                type_='broadcast',
+                name='B',
+                content='b' * 42,
+            ),
+            template_json(
+                SERVICE_ONE_ID,
+                fake_uuid,
+                type_='broadcast',
+                name='C',
+                content='c' * 43,
+            ),
+            template_json(
+                SERVICE_ONE_ID,
+                fake_uuid,
+                type_='broadcast',
+                name='D',
+                # This should be truncated at 40 chars, then have the
+                # trailing space stripped
+                content=('d' * 39) + ' ' + ('d' * 40),
+            ),
+        ]}
+    )
+    page = client_request.get(
+        'main.choose_template',
+        service_id=SERVICE_ONE_ID,
+    )
+    assert [
+        (
+            normalize_spaces(template.select_one('.govuk-link').text),
+            normalize_spaces(template.select_one('.govuk-hint').text),
+        )
+        for template in page.select('.template-list-item')
+    ] == [
+        (
+            'A', 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
+        ),
+        (
+            'B', 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb',
+        ),
+        (
+            'C', 'cccccccccccccccccccccccccccccccccccccccc…',
+        ),
+        (
+            'D', 'ddddddddddddddddddddddddddddddddddddddd…',
+        ),
+    ]
+
+
 def test_choose_template_can_pass_through_an_initial_state_to_templates_and_folders_selection_form(
     client_request,
     mock_get_template_folders,