Best practices for testing web components?

I recently rebuilt a moderately sized jQuery application/component using Lit, with the end result being 6-7 components spread over around 2,000 lines of code.

We currently have no automated testing at all but I'd like to implement it, especially now as the markup/styles have been moved into JavaScript. It's much better overall - but it feels riskier.

But I have no idea where to even begin. Do I set up end to end tests using Playwright on site? Can I test the components individually? Keeping in mind as well that we don't use a build system/any sort of CI.

Just wanted to get people's thoughts/experiences here.