[MAINT] Remove skip markers because tests work again (#1781)

We had issues with a flaky tests, at least partially due to a flaky
server (#1544).
I tried to investigate but found that all tests currently work again. 
While I can see some ways to improve the tests, I want to defer that
until more PRs are merged that affect the same files to avoid needlessly
complicated merge conflicts. At the same time, I'd like to re-enable the
tests to bring back coverage.

Author: PGijsbers

tests/test_evaluations/test_evaluation_functions.py

@@ -262,8 +262,8 @@ def test_list_evaluations_setups_filter_flow(self):
         keys = list(evals["parameters"].values[0].keys())
         assert all(elem in columns for elem in keys)
 
+    # 2026-10-20: Removed skip marker, test just works (#1544)
     @pytest.mark.production_server
-    @pytest.mark.xfail(reason="failures_issue_1544", strict=False)
     def test_list_evaluations_setups_filter_task(self):
         self.use_production_server()
         task_id = [6]

tests/test_flows/test_flow.py

@@ -75,8 +75,8 @@ def test_get_flow(self):
         assert subflow_3.parameters["L"] == "-1"
         assert len(subflow_3.components) == 0
 
+    # 2026-10-20: Removed skip marker, test just works (#1544)
     @pytest.mark.production_server
-    @pytest.mark.xfail(reason="failures_issue_1544", strict=False)
     def test_get_structure(self):
         # also responsible for testing: flow.get_subflow
         # We need to use the production server here because 4024 is not the

tests/test_flows/test_flow_functions.py

@@ -270,14 +270,14 @@ def test_are_flows_equal_ignore_if_older(self):
         )
         assert_flows_equal(flow, flow, ignore_parameter_values_on_older_children=None)
 
+    # 2026-10-20: Removed skip marker, test just works (#1544)
     @pytest.mark.sklearn
     @unittest.skipIf(
         Version(sklearn.__version__) < Version("0.20"),
         reason="OrdinalEncoder introduced in 0.20. "
         "No known models with list of lists parameters in older versions.",
     )
     @pytest.mark.test_server
-    @pytest.mark.xfail(reason="failures_issue_1544", strict=False)
     def test_sklearn_to_flow_list_of_lists(self):
         from sklearn.preprocessing import OrdinalEncoder
 
@@ -521,7 +521,6 @@ def test_delete_flow_success(mock_request, test_files_directory, test_server_v1,
 
 
 @mock.patch.object(requests.Session, "request")
-@pytest.mark.xfail(reason="failures_issue_1544", strict=False)
 def test_delete_unknown_flow(mock_request, test_files_directory, test_server_v1, test_apikey_v1):
     content_file = test_files_directory / "mock_responses" / "flows" / "flow_delete_not_exist.xml"
     mock_request.return_value = create_request_response(

tests/test_runs/test_run_functions.py

@@ -1626,8 +1626,8 @@ def test_get_runs_list_by_filters(self):
         )
         assert len(runs) == 2
 
+    # 2026-10-20: Removed skip marker, test just works (#1544)
     @pytest.mark.production_server
-    @pytest.mark.xfail(reason="failures_issue_1544", strict=False)
     def test_get_runs_list_by_tag(self):
         # We don't have tagged runs on the test server
         self.use_production_server()

tests/test_study/test_study_functions.py

@@ -8,8 +8,8 @@
 from openml.testing import TestBase
 
 
+# 2026-10-20: Removed skip marker, test just works (#1544)
 @pytest.mark.production_server
-@pytest.mark.xfail(reason="failures_issue_1544", strict=False)
 def test_get_study_old():
     study = openml.study.get_study(34)
     assert len(study.data) == 105

tests/test_tasks/test_task_functions.py

@@ -54,8 +54,8 @@ def test__get_estimation_procedure_list(self):
         assert isinstance(estimation_procedures[0], dict)
         assert estimation_procedures[0]["task_type_id"] == TaskType.SUPERVISED_CLASSIFICATION
 
+    # 2026-10-20: Removed skip marker, test just works (#1544)
     @pytest.mark.production_server
-    @pytest.mark.xfail(reason="failures_issue_1544", strict=False)
     def test_list_clustering_task(self):
         self.use_production_server()
         # as shown by #383, clustering tasks can give list/dict casting problems