testing: add more unit tests to increase branch coverage

[mohammed90]

Self-expalantory. We need to add more tests; and I wondered if LLMs could generate tests covering all the logic branches, so this is the result.

Assistance Disclosure

I used Amp to generate the tests, tweaked few by hand, and fixed the bug by hand. The generated code will not be taken and accepted at face value. Changes to the source code (not tests) by the agent will not be accepted. Only the tests cases with study of coverage.

Prompt:

Study the full codebase of the project. Write unit tests to validate the functionality and ensure robustness. The tests should check for the intended behavior, not the behavior as written. It is possible the existing code base has an unknown defect, for which we need the unit tests to uncover. Write the unit tests.