Simplify torchscript test and port unit-test to pytest

[zhiqwang]

No description provided.

[codecov]

Codecov Report

Merging #152 (1c71213) into master (6f8cbf9) will decrease coverage by 0.74%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #152      +/-   ##
==========================================
- Coverage   84.19%   83.44%   -0.75%     
==========================================
  Files          12       12              
  Lines         797      761      -36     
==========================================
- Hits          671      635      -36     
  Misses        126      126              

Flag	Coverage Δ
unittests	83.44% <100.00%> (-0.75%)	⬇️

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Impacted Files	Coverage Δ
test/test_image_utils.py	100.00% <100.00%> (ø)
test/test_torchscript.py	100.00% <100.00%> (ø)
test/test_utils.py	100.00% <100.00%> (ø)

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