test: add DTO tests

[faustbrian]

Resolves #192

[codecov]

Codecov Report

Merging #193 into master will increase coverage by 1.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   80.93%   82.14%   +1.20%     
==========================================
  Files          26       26              
  Lines         745      745              
  Branches       93       93              
==========================================
+ Hits          603      612       +9     
+ Misses        141      132       -9     
  Partials        1        1              

Impacted Files	Coverage Δ
src/services/client.ts	86.75% <0.00%> (+1.32%)	⬆️
src/dto/transaction.ts	90.24% <0.00%> (+17.07%)	⬆️

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