Add validation methods in tasks

[zhiqwang]

Fixing #59

[codecov]

Codecov Report

Merging #93 (5b461e1) into master (e827589) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   83.31%   83.35%   +0.04%     
==========================================
  Files           8        8              
  Lines         773      775       +2     
==========================================
+ Hits          644      646       +2     
  Misses        129      129              

Flag	Coverage Δ
unittests	83.35% <100.00%> (+0.04%)	⬆️

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Impacted Files	Coverage Δ
test/test_data_pipeline.py	100.00% <100.00%> (ø)
test/test_engine.py	100.00% <100.00%> (ø)

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