test: add tests for large offsets in datastore

tests/system/test_system.py

@@ -405,6 +405,18 @@ def test_query_offset_timestamp_keys(self):
         offset_w_limit = list(query.fetch(offset=offset, limit=max_offset))
         self.assertEqual(offset_w_limit, all_w_limit[offset:])
 
+    def test_query_large_offset_timestamp_keys(self):
+        # See issue #4675
+        max_all = 10000
+        offset = 21
+        max_offset = max_all - offset
+        query = self.CLIENT.query(kind="timestamp_key")
+        all_w_limit = list(query.fetch(limit=max_all))
+        self.assertEqual(len(all_w_limit), max_all)
+
+        offset_w_limit = list(query.fetch(offset=offset, limit=max_offset))
+        self.assertEqual(offset_w_limit, all_w_limit[offset:])
+
     def test_query_paginate_with_offset(self):
         page_query = self._base_query()
         page_query.order = "appearances"
@@ -429,6 +441,24 @@ def test_query_paginate_with_offset(self):
         self.assertEqual(entities[1]["name"], "Jon Snow")
         self.assertEqual(entities[2]["name"], "Arya")
 
+    def test_query_paginate_with_large_offset(self):
+        page_query = self._base_query()
+        page_query.order = "appearances"
+        offset = 21
+        limit = 3
+        iterator = page_query.fetch(limit=limit, offset=offset)
+
+        # Fetch characters.
+        page = six.next(iterator.pages)
+        entities = list(page)
+        cursor = iterator.next_page_token
+        self.assertEqual(len(entities), 0)
+
+        # Fetch next set of characters.
+        new_iterator = page_query.fetch(limit=limit, offset=0, start_cursor=cursor)
+        entities = list(new_iterator)
+        self.assertEqual(len(entities), 0)
+
     def test_query_paginate_with_start_cursor(self):
         page_query = self._base_query()
         page_query.order = "appearances"