Be sure that the browser window is in focus while tests are running.
Individual files can be tested by running `gulp collectTests -f [Tone class name]` which will update the test/Main.js with the given class' tests. You can then refresh the `test/index.html` page to rerun those tests.
You can also test groups of classes by folder by adding another flag. For example to test all of the signals run `gulp collectTests --signal`. or the shorthand form: `gulp collectTests -s`.
The tests target the latest [specification](https://webaudio.github.io/web-audio-api/) and not any specific browser. I have been keeping a list of which features browsers/versions currently support in `test/helper/Supports.js`. Some tests are only conditionally run if that feature is supported on the platform.