test: Add opener implementations for tests

[effigies]

Pulled out of #282 (and expanded) to keep that one focused.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.32%. Comparing base (1560a88) to head (2b67763).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #283      +/-   ##
==========================================
- Coverage   87.33%   87.32%   -0.02%     
==========================================
  Files          49       49              
  Lines        3624     3620       -4     
  Branches      593      593              
==========================================
- Hits         3165     3161       -4     
  Misses        449      449              
  Partials       10       10              

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