Add a unit testing guide for maintainers, contributors, and coding assistants.
The guide should provide language-agnostic principles and stack-specific guidance for Python, Python/Qt, Rust, and Svelte/TypeScript/JavaScript, including what to test, what to avoid, regression testing, and UI testing scope.
Add a unit testing guide for maintainers, contributors, and coding assistants.
The guide should provide language-agnostic principles and stack-specific guidance for Python, Python/Qt, Rust, and Svelte/TypeScript/JavaScript, including what to test, what to avoid, regression testing, and UI testing scope.