[test-runner] Support per-test progress instead of per-file

[acelaya]

First of all, apologies if this has been discussed somewhere. I was not able to find an issue or discussion around this subject.

I would like to know if it's possible, or has been discussed in the past, that web-test-runner reports/updates progress on a per-test basis, instead of per-file.

We are in the process of migrating our test suite away from karma, and our current workflow involves manually bundling our tests with rollup into a single bundle file (as they use TypeScript, JSX with preact and whatnot), and then feed that file to the test runner.

With karma it was possible to see the tests being run in real time, while with web-test-runner it seems like nothing is happening until all tests in the bundle have been run and the output is dumped all at once.

We know it's possible to use esbuild and rollup plugins directly with web-test-runner, which would probably mitigate this problem, but our bundling is relatively complex (including babel and custom babel plugins) and we haven't been able to make it work all together without a bundling step before running web-test-runner.

Thanks.