Add test for cached elements, use cache setters and fix return in doc…

… block

src/Models/BaseElement.php

@@ -676,7 +676,8 @@ public function getAreaRelationName()
             }
         }
 
-        $this->cacheData['area_relation_name'] = $result;
+        $this->setAreaRelationNameCache($result);
+
         return $result;
     }
 

src/Models/ElementalArea.php

@@ -112,7 +112,7 @@ public function setOwnerPageCached(DataObject $page)
 
     /**
      * A cache-aware accessor for the elements
-     * @return ArrayList|DataList
+     * @return ArrayList|DataList|BaseElement[]
      */
     public function Elements()
     {
@@ -206,7 +206,7 @@ public function getOwnerPage()
                 $page = Versioned::get_by_stage($class, $currentStage)->filter($areaID, $this->ID)->first();
 
                 if ($page) {
-                    $this->cacheData['owner_page'] = $page;
+                    $this->setOwnerPageCached($page);
                     return $page;
                 }
             }

tests/ElementalAreaTest.php

@@ -132,4 +132,18 @@ public function testUnsavedRelationListOfElementsReturnsEmptyArrayList()
         $this->assertInstanceOf(ArrayList::class, $result);
         $this->assertEmpty($result);
     }
+
+    public function testElementsListIsCached()
+    {
+        $area = new ElementalArea();
+
+        $element = new ElementContent();
+        $element->HTML = 'Test';
+
+        $elements = new ArrayList([$element]);
+
+        $area->setElementsCached($elements);
+
+        $this->assertSame($elements, $area->Elements());
+    }
 }