add unit test for textsnake

[cuhk-hbsun]

fix #57

[codecov]

Codecov Report

Merging #61 (193e57e) into main (344cc9a) will decrease coverage by 0.06%.
The diff coverage is n/a.

❗ Current head 193e57e differs from pull request most recent head e85937f. Consider uploading reports for the commit e85937f to get more accurate results

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   76.60%   76.53%   -0.07%     
==========================================
  Files         104      104              
  Lines        6261     6261              
  Branches      919      919              
==========================================
- Hits         4796     4792       -4     
- Misses       1251     1252       +1     
- Partials      214      217       +3     

Flag	Coverage Δ
unittests	76.53% <ø> (-0.07%)	⬇️

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Impacted Files	Coverage Δ
mmocr/core/mask.py	88.63% <0.00%> (-6.82%)	⬇️
...cr/models/textdet/detectors/text_detector_mixin.py	81.81% <0.00%> (-3.04%)	⬇️

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