Adding no rebuild test

test/image_test.py

@@ -752,6 +752,7 @@ def f(self):
 
 class FooInstance:
     bar: str = "5"
+    barbar: str = "2"
 
     @build()
     def build_func(self):
@@ -774,6 +775,23 @@ def test_image_cls_var_rebuild(client, servicer):
     assert image_id != image_id2
 
 
+def test_image_cls_var_no_rebuild(client, servicer):
+    rebuild_app = App()
+    image_id = -1
+    rebuild_app.cls(image=Image.debian_slim())(FooInstance)
+    with rebuild_app.run(client=client):
+        image_id = list(servicer.images.keys())[-1]
+    rebuild_app.cls(image=Image.debian_slim())(FooInstance)
+    with rebuild_app.run(client=client):
+        image_id2 = list(servicer.images.keys())[-1]
+    FooInstance.barbar = "22"
+    rebuild_app.cls(image=Image.debian_slim())(FooInstance)
+    with rebuild_app.run(client=client):
+        image_id3 = list(servicer.images.keys())[-1]
+    assert image_id == image_id2
+    assert image_id2 == image_id3
+
+
 def test_image_build_snapshot(client, servicer):
     with cls_app.run(client=client):
         image_id = list(servicer.images.keys())[-1]