I can collect return values

tests/test_observable.py

@@ -1,6 +1,6 @@
 import pytest
 
-from myutils.observable import NotObservableError, make_observable, bind
+from myutils.observable import NotObservableError, make_observable, bind, collect_return_values
 
 
 # Test fixtures
@@ -170,4 +170,38 @@ def test_i_can_preserve_original_class_behavior():
   assert demo.get_double() == 10
   
   # Test that isinstance still works
-  assert isinstance(demo, Demo)
+  assert isinstance(demo, Demo)
+
+
+def test_i_can_collect_the_updates():
+  demo = Demo()
+  make_observable(demo)
+  
+  bind(demo, 'number', lambda old, new: new)
+  bind(demo, 'number', lambda old, new: new * 2)
+  
+  demo.number = 5
+  assert collect_return_values(demo) == [5, 10]
+  
+  # another time to make sure there is no side effect
+  demo.number = 10
+  assert collect_return_values(demo) == [10, 20]
+
+
+def test_i_cannot_collect_updates_before_making_observable():
+  demo = Demo()
+  
+  with pytest.raises(NotObservableError) as exc_info:
+    collect_return_values(demo)
+  
+  assert "must be made observable" in str(exc_info.value).lower()
+
+
+def test_i_can_collect_none():
+  demo = Demo()
+  make_observable(demo)
+  
+  bind(demo, 'number', lambda old, new: None)
+  
+  demo.number = 5
+  assert collect_return_values(demo) == [None]