Refactor defaultdict tests

[yukinarit]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.59%. Comparing base (83d9308) to head (49aac4e).
⚠️ Report is 325 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #477      +/-   ##
==========================================
+ Coverage   89.48%   89.59%   +0.10%     
==========================================
  Files          12       12              
  Lines        1931     1931              
  Branches      400      400              
==========================================
+ Hits         1728     1730       +2     
+ Misses        148      147       -1     
+ Partials       55       54       -1     

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