Use hypothesis (#5759)

* Use hypothesis

* Allow int64 array interface for groups

* Add packages to Windows CI

* Add to travis

* Make sure device index is set correctly

* Fix dask-cudf test

* appveyor

tests/python-gpu/test_gpu_pickling.py

@@ -4,9 +4,13 @@ import unittest
 import numpy as np
 import subprocess
 import os
+import sys
 import json
 import pytest
 
+sys.path.append("tests/python")
+import testing as tm
+
 import xgboost as xgb
 from xgboost import XGBClassifier
 
@@ -90,7 +94,6 @@ class TestPickling(unittest.TestCase):
         )
         status = subprocess.call(args, env=env)
         assert status == 0
-
         os.remove(model_path)
 
     def test_pickled_predictor(self):