Add test to improve code coverage.

[lijunzh]

Fix #12

[codecov]

Codecov Report

Merging #14 into master will increase coverage by 11.46%.
The diff coverage is 57.14%.

@@             Coverage Diff             @@
##           master      #14       +/-   ##
===========================================
+ Coverage   42.35%   53.81%   +11.46%     
===========================================
  Files          22       21        -1     
  Lines         935      825      -110     
  Branches      107       98        -9     
===========================================
+ Hits          396      444       +48     
+ Misses        538      381      -157     
+ Partials        1        0        -1     

Impacted Files	Coverage Δ
src/yews/train/functional.py	21.87% <0.00%> (+4.16%)	⬆️
src/yews/models/cpic.py	100.00% <100.00%> (+83.33%)	⬆️
src/yews/transforms/transforms.py	100.00% <100.00%> (+14.28%)	⬆️
src/yews/datasets/utils.py	100.00% <0.00%> (+9.19%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 59b9e8c...62d6ca3. Read the comment docs.