Add 503 page for SERVICE_ENABLED=False

* Add custom error page for 503

Render a message to users if we've disabled the service and they try to
access it.

Author: gpeng

manage_breast_screening/core/jinja2/503.jinja

@@ -0,0 +1,10 @@
+{% extends "layout-app.jinja" %}
+
+{% block content %}
+<div class="nhsuk-grid-row">
+    <div class="nhsuk-grid-column-two-thirds">
+        <h1>Sorry, this service is unavailable</h1>
+        <p>The service is unavailable due to planned maintenance.</p>
+    </div>
+</div>
+{% endblock %}

manage_breast_screening/core/middleware/service_enabled.py

@@ -2,6 +2,7 @@
 
 from django.conf import settings
 from django.http import HttpResponse
+from django.shortcuts import render
 
 from manage_breast_screening.core.decorators import is_service_enabled_exempt
 
@@ -29,4 +30,4 @@ def process_view(
         if is_service_enabled_exempt(view_func):
             return None
 
-        return HttpResponse("Service unavailable", status=503)
+        return render(request, "503.jinja", status=503)

manage_breast_screening/core/tests/middleware/test_service_enabled.py

@@ -31,6 +31,7 @@ def test_service_disabled_returns_503(self, settings):
         resp = mw.process_view(request, lambda r: None, (), {})
         assert resp is not None
         assert resp.status_code == 503
+        assert b"Sorry, this service is unavailable" in resp.content
 
     def test_service_disabled_exempt_view_allows_request(self, settings):
         settings.SERVICE_ENABLED = False