Interesting testing techniques for frontend development

I want to share with you the experience of using several interesting testing techniques during the development of frontend applications(ex. this website lcg.kz). In the last project, we experimented with different approaches and would like to hear your opinion and experience.

A/B interface testing: What tools and approaches do you use to evaluate the effectiveness of the user interface?

Performance testing: Which tools do you prefer to check the speed of loading and rendering pages?

Unit testing of components: Which frameworks do you use to test individual components of an application?

I will be grateful for your ideas and advice on these issues! Let’s discuss it.