add test & refactor

[ddddddO]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (78a2f15) 86.15% compared to head (58be276) 87.03%.

Files	Patch %	Lines
simple_tree_walker.go	80.00%	0 Missing and 3 partials ⚠️
pipeline_tree.go	50.00%	2 Missing ⚠️
pipeline_tree_walker.go	75.00%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #260      +/-   ##
==========================================
+ Coverage   86.15%   87.03%   +0.88%     
==========================================
  Files          26       26              
  Lines        1466     1458       -8     
==========================================
+ Hits         1263     1269       +6     
+ Misses        155      141      -14     
  Partials       48       48              

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