Test coverage

Test coverage is somewhat spotty right now. Plenty of the core pieces are covered, along with actual bugs that were discovered by usage, but there are plenty of obvious gaps in our current verification.

Any contribution to increase coverage of the pytest tests is welcome.

Note that these tests do not have a usable py command, and so need to be structured to not rely on that - plenty of mocks, monkey-patching and directly importing commands is intended!

(For tests that can only be run after the full app is compiled/installed, create a new issue describing the scenario and why you think it wouldn't be valid as a unit test.)

首先检查现有的 pytest 测试套件，并确定一个尚未覆盖且可进行单元测试的核心区域；该 issue 未指定具体的文件或入口点。在不依赖可用的 py 命令的情况下组织测试，并根据需要使用 mock、monkey-patching 或直接导入命令。完成的标准是：为选定的缺口添加有针对性的覆盖，并在不编译或安装完整应用的情况下保持测试有效。