add test that covers loading cache

test env assumes strings are in cache, so use
redis.set with strings (assume lib does encoding)

inventory_provider/routes/lg.py

@@ -125,7 +125,7 @@ def routers(access):
             result = json.dumps(result)
 
             # cache this data for the next call
-            redis.set(cache_key, result.encode('utf-8'))
+            redis.set(cache_key, result)
 
     if not result:
         return Response(

test/test_lg_routes.py

@@ -23,6 +23,11 @@ def test_public_routers(client):
     assert all(r['type'] == 'CORE' for r in response_data)
 
 
+def test_with_cache(client):
+    test_public_routers(client)
+    test_public_routers(client)
+
+
 @pytest.mark.skip(reason='IMS INTERNAL vs CORE calcualtion is not clear')
 def test_internal_routers(client):
     rv = client.get(