How to test a wasm app fully?

This might not fully be rust specific, but using cargo to test is so convenient that I kinda want to use it... So, I have this desktop app which is well tested, which I'm converting to a wasm app. There's not much coding needed (after I moved IO up the call chain), so in turn the library making up the code for the wasm app is well tested. But, the full "app" consists of some other code as well, some html and quite some JS. I'd really like to fully test this (if at all possible with different ...