Unit is related to Step. Step is a synonym of Stage. Stage is related to Construction. Construction is related to Stone. 
Accounting is a type of System. Accounting is related to Test. Testing is a form of Test. 
Unit <--RelatedTo--> Step <--Synonym--> Stage <--RelatedTo--> Construction <--RelatedTo--> Stone 
System <--IsA-- Accounting <--RelatedTo--> Test <--FormOf-- Testing 