tests: Add more coinjoin related tests

[HashEngineering]

Issue being fixed or feature implemented

What was done?

How Has This Been Tested?

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (eb4e227) 48.47% compared to head (5397e26) 48.53%.

Additional details and impacted files

@@                  Coverage Diff                   @@
##             feature-coinjoin     #243      +/-   ##
======================================================
+ Coverage               48.47%   48.53%   +0.05%     
- Complexity               7446     7467      +21     
======================================================
  Files                     451      451              
  Lines                   50127    50127              
  Branches                 7128     7128              
======================================================
+ Hits                    24300    24328      +28     
+ Misses                  23087    23068      -19     
+ Partials                 2740     2731       -9     

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