Emitting progress on test in public API (feature request)

### Expected behaviour
When tests are executed in the browser(s) I would like to be able to get notification after each test finished (ok/error) in the public API. This could be bubbled up to the Server level and accessible by:

`server.on('test_finished', function(details) { ...})`

or by exposing other API elsewhere, but with similar functionality. This would be similar to the console logs appearing one-by-one after each test finishes.

If such an API would be accepted then I can prepare a PR with implementation & relevant tests.

### Actual behaviour
When tests execute there is no notification about this.

### Environment Details
Examined latest source code on github.

Trace how browser test completion and the existing console logs reach the Server-level public API. Define the event payload for successful and failed tests, then add relevant tests for one notification after each test finishes. Done means consumers can subscribe through the public API and receive each test result.

Written by the indexing model from the issue text.