[Improve] Update unittest

[dreamerlin]

This PR

1. Improve unittest coverge
2. Create tests/test_runtime

[codecov]

Codecov Report

Merging #322 (9e7a829) into master (76819e4) will increase coverage by 1.34%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #322      +/-   ##
==========================================
+ Coverage   82.35%   83.70%   +1.34%     
==========================================
  Files          95       95              
  Lines        6768     6768              
  Branches     1095     1095              
==========================================
+ Hits         5574     5665      +91     
+ Misses        987      897      -90     
+ Partials      207      206       -1     

Flag	Coverage Δ
unittests	83.68% <ø> (+1.34%)	⬆️

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Impacted Files	Coverage Δ
mmaction/core/evaluation/accuracy.py	92.85% <0.00%> (+4.28%)	⬆️
mmaction/core/evaluation/eval_hooks.py	83.47% <0.00%> (+26.44%)	⬆️
mmaction/apis/test.py	72.09% <0.00%> (+58.13%)	⬆️

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