'Tests that to_python of value column is called'

def test_to_python(self):

    column = columns.List(JsonTestColumn)
    val = [1, 2, 3]
    db_val = column.to_database(val)
    self.assertEqual(db_val, [json.dumps(v) for v in val])
    py_val = column.to_python(db_val)
    self.assertEqual(py_val, val)
