Give better indication of when a test passed or failed #85
Description
The test gives clear feedback when it either reaches the test page successfully or rejects the access. If something goes wrong and the page doesn't redirect (see Issue #84) it can be hard to tell that it has failed.
We need to be careful addressing this, because the test is handled the same way as worker requests are handled. We don't want to provide any information we're not willing to expose to workers. One possibility is to have a separate frame with instructions or extra diagnostic information.