Raise error if getting complaints page with invalid page param

If the `page` parameter passed to the `platform-admin/complaints`
pageis not an integer, we should return a `404` error page.

app/main/views/jobs.py

@@ -199,7 +199,7 @@ def get_notifications(service_id, message_type, status_override=None):
     # TODO get the api to return count of pages as well.
     page = get_page_from_request()
     if page is None:
-        abort(404, "Invalid page argument ({}) reverting to page 1.".format(request.args['page'], None))
+        abort(404, "Invalid page argument ({}).".format(request.args.get('page')))
     if message_type not in ['email', 'sms', 'letter']:
         abort(404)
     filter_args = parse_filter_args(request.args)

app/main/views/platform_admin.py

@@ -1,7 +1,7 @@
 import itertools
 from datetime import datetime
 
-from flask import render_template, request, url_for
+from flask import abort, render_template, request, url_for
 from flask_login import login_required
 
 from app import (
@@ -15,6 +15,7 @@ from app.statistics_utils import get_formatted_percentage
 from app.utils import (
     generate_next_dict,
     generate_previous_dict,
+    get_page_from_request,
     user_is_platform_admin,
 )
 
@@ -194,7 +195,10 @@ def platform_admin_services():
 @login_required
 @user_is_platform_admin
 def platform_admin_list_complaints():
-    page = int(request.args.get('page', 1))
+    page = get_page_from_request()
+    if page is None:
+        abort(404, "Invalid page argument ({}).".format(request.args.get('page')))
+
     response = complaint_api_client.get_all_complaints(page=page)
 
     prev_page = None

tests/app/main/views/test_platform_admin.py

@@ -706,6 +706,17 @@ def test_should_show_complaints_with_next_previous(mocker, client, platform_admi
     assert 'page 1' in prev_page_link.text.strip()
 
 
+def test_platform_admin_list_complaints_returns_404_with_invalid_page(mocker, client, platform_admin_user):
+    mock_get_user(mocker, user=platform_admin_user)
+    client.login(platform_admin_user)
+
+    mocker.patch('app.complaint_api_client.get_all_complaints', return_value={'complaints': [], 'links': {}})
+
+    response = client.get(url_for('main.platform_admin_list_complaints', page='invalid'))
+
+    assert response.status_code == 404
+
+
 @pytest.mark.parametrize('number, total, threshold, result', [
     (0, 0, 0, False),
     (1, 1, 0, True),