fix(wasm): Check for browser bundle existence before running tests

[lobsterkatie]

As of #4048, it's more likely that one might try to run the full test suite without having built the browser bundle. Since the wasm tests rely on it, this adds a check before they run, along with an error message letting the user know why things aren't working.

[github-actions]

size-limit report

Path	Size
@sentry/browser - CDN Bundle (gzipped)	22.36 KB (+0.01% 🔺)
@sentry/browser - Webpack	23.24 KB (0%)
@sentry/react - Webpack	23.27 KB (0%)
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	29.8 KB (+0.01% 🔺)

[iker-barriocanal]

This looks good, but it'd be better if we do something to prevent having this error. Having a check for this before running the tests that build the browser CDN bundle is a better choice IMO.

[rhcarvalho]

Having a check for this before running the tests that build the browser CDN bundle is a better choice IMO.

And that should also prevent running the tests accidentally against a stale build, so +1 👍

[lobsterkatie]

Having a check for this before running the tests that build the browser CDN bundle is a better choice IMO.

And that should also prevent running the tests accidentally against a stale build, so +1 👍

Yeah, I thought about doing that, but (for once!) I didn't want to over-engineer things, and I also wondered at whether there might not be times when you'd want to be the one in control of that rather than a script forcing it on you.

Seeing as these tests have been there the better part of year and we've yet to run into the problem (that I know of), I'm going to merge this now and we can keep the other in mind if this ever crops up again.

If either of you feels strongly about this, happy to revisit it.