test(transaction-pool-worker): increase unit test coverage

[sebastijankuzner]

Summary

Checklist

• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.61%. Comparing base (fe6f3b9) to head (42e6276).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1317      +/-   ##
===========================================
+ Coverage    55.81%   56.61%   +0.79%     
===========================================
  Files          967      970       +3     
  Lines        64426    64861     +435     
  Branches      1580     1674      +94     
===========================================
+ Hits         35960    36720     +760     
+ Misses       28237    27903     -334     
- Partials       229      238       +9     

Flag	Coverage Δ
contracts	97.74% <ø> (?)
packages	56.32% <ø> (+0.51%)	⬆️

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