Add unit test for refcount of cypclass loop variables

tests/run/cypclass_iteration.pyx

@@ -91,4 +91,27 @@ def test_stack_refcount():
     if Cy_GETREF(s) != 2:
         return -3
 
-    return 0
+    return 0
\ No newline at end of file
+
+def test_loop_variable_refcount():
+    """
+    >>> test_loop_variable_refcount()
+    Value destroyed
+    0
+    """
+    s = Stack()
+    s.push(Value())
+
+    for val in s:
+        refcnt = Cy_GETREF(val)
+        if refcnt != 3:
+            print(refcnt)
+            return -1
+
+    for val in s:
+        refcnt = Cy_GETREF(val)
+        if refcnt != 3:
+            print(refcnt)
+            return -1
+
+    return 0