Add test suite

Lot of moving parts doing weird things. Inline comment documentation is helpful, but a test suite here would not only help to mitigate bugs but would also be very helpful as supplementary documentation

The issue names no files, tests, or entry points. Start by inspecting the repository's Python modules and existing test configuration, then identify the moving parts that need coverage. Done means a maintainable test suite exists and documents expected behavior while helping detect regressions.

Written by the indexing model from the issue text.