Add classification backbones unit test

[jaegukhyun]

Summary

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have added e2e tests for validation.
• I have added the description of my changes into CHANGELOG in my target branch (e.g., CHANGELOG in develop).​
• I have updated the documentation in my target branch accordingly (e.g., documentation in develop).
• I have linked related issues.

License

• I submit my code changes under the same Apache License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2023 Intel Corporation
# SPDX-License-Identifier: Apache-2.0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.77%. Comparing base (25fc3e1) to head (f042b4c).
Report is 1 commits behind head on v2.

Additional details and impacted files

@@            Coverage Diff             @@
##               v2    #3065      +/-   ##
==========================================
+ Coverage   59.34%   61.77%   +2.42%     
==========================================
  Files         253      253              
  Lines       14984    14826     -158     
==========================================
+ Hits         8893     9159     +266     
+ Misses       6091     5667     -424     

Flag	Coverage Δ
py310	61.77% <ø> (+2.42%)	⬆️
py311	61.77% <ø> (+2.42%)	⬆️

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