add cell manipulation helper unit tests

Author: Joe Jevnik

tests/cloudpickle_test.py

@@ -38,7 +38,7 @@
 from io import BytesIO
 
 import cloudpickle
-from cloudpickle.cloudpickle import _find_module
+from cloudpickle.cloudpickle import _find_module, _make_empty_cell, cell_set
 
 from .testutils import subprocess_pickle_echo
 
@@ -494,6 +494,19 @@ def example():
                    "'))()")
         assert not subprocess.call([sys.executable, '-c', command])
 
+    def test_cell_manipulation(self):
+        cell = _make_empty_cell()
+
+        with pytest.raises(ValueError):
+            cell.cell_contents
+
+        ob = object()
+        cell_set(cell, ob)
+        self.assertEqual(
+            cell.cell_contents is ob,
+            msg='cell contents not set correctly',
+        )
+
 
 if __name__ == '__main__':
     unittest.main()