test: Improve test coverage for CLI schema introspection

[allenporter]

Adds unit tests covering CLI schema introspection, parameter lookup, and error cases in schema.py.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.58%. Comparing base (e60d657) to head (c2500b3).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
+ Coverage   82.09%   82.58%   +0.48%     
==========================================
  Files          30       30              
  Lines        3100     3100              
==========================================
+ Hits         2545     2560      +15     
+ Misses        555      540      -15     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.