Test now only executed for sklearn>=0.20.

Author: PGijsbers

tests/test_flows/test_flow_functions.py

@@ -1,5 +1,9 @@
 from collections import OrderedDict
 import copy
+import unittest
+
+from distutils.version import LooseVersion
+import sklearn
 
 import openml
 from openml.testing import TestBase
@@ -222,6 +226,9 @@ def test_are_flows_equal_ignore_if_older(self):
                           ignore_parameter_values_on_older_children=flow_upload_date)
         assert_flows_equal(flow, flow, ignore_parameter_values_on_older_children=None)
 
+    @unittest.skipIf(LooseVersion(sklearn.__version__) < "0.20",
+                     reason="OrdinalEncoder introduced in 0.20. "
+                            "No known models with list of lists parameters in older versions.")
     def test_sklearn_to_flow_list_of_lists(self):
         from sklearn.preprocessing import OrdinalEncoder
         ordinal_encoder = OrdinalEncoder(categories=[[0, 1], [0, 1]])