Adding launch.json is generally not done because debugging is very use-case specific. This particular JSON doesn't really take advantage of breakpoint debugging too. It's just running the tests from what I see. What may make sense is a launch.tmpl.json that contains an example configuration and also implement debugging as featured in pptr.dev. This would help developers of Puppeteer, but also model current recommendations.

VsCode attaches a debugger to node (and all spawned processes) when running from launch.json so breakpoints put in puppeteer or test do stop. Implementing the thing in the debugging page is for users of puppeteer, not contributes like this PR is aimed for.