Move Python testing utilities into xgboost module. (#8379)

- Add typehints.
- Fixes for pylint.

Co-authored-by: Hyunsu Philip Cho <chohyu01@cs.washington.edu>

tests/python/test_spark/test_data.py

@@ -4,7 +4,8 @@ from typing import List
 import numpy as np
 import pandas as pd
 import pytest
-import testing as tm
+
+from xgboost import testing as tm
 
 if tm.no_spark()["condition"]:
     pytest.skip(msg=tm.no_spark()["reason"], allow_module_level=True)

tests/python/test_spark/test_spark_local.py

@@ -6,10 +6,9 @@ import uuid
 
 import numpy as np
 import pytest
-import testing as tm
 
 import xgboost as xgb
-from xgboost import testing
+from xgboost import testing as tm
 
 if tm.no_spark()["condition"]:
     pytest.skip(msg=tm.no_spark()["reason"], allow_module_level=True)
@@ -38,7 +37,7 @@ from .utils import SparkTestCase
 
 logging.getLogger("py4j").setLevel(logging.INFO)
 
-pytestmark = testing.timeout(60)
+pytestmark = tm.timeout(60)
 
 
 class XgboostLocalTest(SparkTestCase):

tests/python/test_spark/test_spark_local_cluster.py

@@ -6,7 +6,8 @@ import uuid
 
 import numpy as np
 import pytest
-import testing as tm
+
+from xgboost import testing as tm
 
 if tm.no_spark()["condition"]:
     pytest.skip(msg=tm.no_spark()["reason"], allow_module_level=True)

tests/python/test_spark/utils.py

@@ -6,9 +6,10 @@ import tempfile
 import unittest
 
 import pytest
-import testing as tm
 from six import StringIO
 
+from xgboost import testing as tm
+
 if tm.no_spark()["condition"]:
     pytest.skip(msg=tm.no_spark()["reason"], allow_module_level=True)
 if sys.platform.startswith("win") or sys.platform.startswith("darwin"):