chore: import upstream snapshot with attribution

tests/python/common/backend/test_set_default_backend.py

@@ -0,0 +1,12 @@
+import os
+import unittest
+
+import backend as F
+
+
+def test_set_default_backend():
+    default_dir = os.path.join(os.path.expanduser("~"), ".dgl_unit_test")
+    F.set_default_backend(default_dir, "pytorch")
+
+    # make sure the config file was created
+    assert os.path.exists(os.path.join(default_dir, "config.json"))