add tests for SBDataset

[pmeier]

No description provided.

[codecov]

Codecov Report

Merging #3467 (d0c635e) into master (b266c2f) will increase coverage by 0.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3467      +/-   ##
==========================================
+ Coverage   76.13%   76.41%   +0.28%     
==========================================
  Files         105      105              
  Lines        9703     9697       -6     
  Branches     1556     1556              
==========================================
+ Hits         7387     7410      +23     
+ Misses       1836     1805      -31     
- Partials      480      482       +2     

Impacted Files	Coverage Δ
torchvision/transforms/_transforms_video.py	88.88% <0.00%> (-0.35%)	⬇️
torchvision/models/mobilenetv2.py	86.95% <0.00%> (-0.28%)	⬇️
torchvision/transforms/_functional_video.py	95.23% <0.00%> (-0.22%)	⬇️
torchvision/datasets/sbd.py	81.66% <0.00%> (+48.33%)	⬆️

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