Tip calculator made with Tailwind and tested + Vitest for unit testing

This was my first tailwind project, also I never have done unit testing until now.

• can you give me some advice for writing tests ?
• what are some common questions I should do to myself when I'm writing tests?
• Is there something like a testing template, like the readMe template that Frontend Mentor gives in their projects, so I can learn to do them better?