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.

• This file is over 20k lines long, and 400kB

• It is nested over 10 levels deep in many places

• There is no naming consistency. The original file used BEM, but now it switches randomly between whatever the devs felt like at the time. There are random contractions all over the place (eg, a parent container might have the class payment-items, but the children are p-item)

• There is no style consistency. It switches randomly between kebab case, camel case, snake case, a mix of kebab and snake case (!!) or no case at all (just one long word with no separators). A parent element might use one case, but then the child element will use a different case for the exact same term