Fix dltensor operator tests (#3984)

* Fix dltensor operator tests (missing imports)
* Fix backend_impl shadowing Pipeline import

Signed-off-by: Kamil Tokarski <[email protected]>

Author: stiepan

dali/test/python/test_dltensor_operator.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2019, NVIDIA CORPORATION. All rights reserved.
+# Copyright (c) 2019, 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -27,13 +27,15 @@
 def setup_pytorch():
     global torch_dlpack
     global torch
-    import torch as torch
+    import torch
+    import torch.utils.dlpack as torch_dlpack
     global torch_stream
     torch_stream = torch.cuda.Stream()
 
 
 def setup_mxnet():
     global mxnd
+    from mxnet import ndarray as mxnd
 
 
 def setup_cupy():

dali/test/python/test_external_source_pytorch_dlpack.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved.
+# Copyright (c) 2020, 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,8 +16,8 @@
 import nvidia.dali.fn as fn
 import nvidia.dali.ops as ops
 import torch
-from nvidia.dali import Pipeline
 from nvidia.dali.backend_impl import *  # noqa: F401, F403
+from nvidia.dali import Pipeline
 from torch.utils.dlpack import to_dlpack, from_dlpack
 
 from test_utils import check_output