add parallel test case on cached elements

tests/test_element.py

@@ -2,6 +2,7 @@
 import pytest
 from requests import HTTPError
 
+from arkindex_worker.cache import CachedElement
 from arkindex_worker.models import Element
 
 
@@ -405,10 +406,11 @@ def test_setattr_setitem():
 
 
 def test_element_polygon():
-    element = Element(
-        {"zone": {"polygon": [[0, 0], [181, 0], [181, 240], [0, 240], [0, 0]]}}
-    )
-    assert element.polygon == [[0, 0], [181, 0], [181, 240], [0, 240], [0, 0]]
+    polygon = [[0, 0], [181, 0], [181, 240], [0, 240], [0, 0]]
+    element = Element({"zone": {"polygon": polygon}})
+    cached_element = CachedElement(polygon=polygon)
+    assert element.polygon == polygon
+    assert element.polygon == cached_element.polygon
 
 
 def test_element_no_polygon():