Add test coverage for #453

These tests are passing without errors or deprecations currently.

tests/TestCase/DateTime/AddTest.php

@@ -270,6 +270,17 @@ public function testAddWeek($class)
         });
     }
 
+    /**
+     * @dataProvider classNameProvider
+     * @return void
+     */
+    public function testAddWeeksStartOfWeek($class)
+    {
+        $this->assertSame(5, (new $class(2024, 7, 2,))->addWeeks(1)->startOfWeek()->day);
+
+        $this->assertSame(14, $class::createFromDate(2024, 7, 2,)->addWeeks(1)->endOfWeek()->day);
+    }
+
     /**
      * @dataProvider classNameProvider
      * @return void