Calling test() multiple times in the same test file is not actually
valid, and can cause the following test to hang forever. So let's stop
doing that in the one test that did so, and also prevent the same
mistake happening again. :^)
Throwing an exception on subsequent test() calls means that we don't
hang, the test will fail with missing output, and we get a log message
explaining why.
Previously, we used `on_load_finish` to determine when the text test
was completed. This method did not allow testing of async functions
because there was no way to indicate that the runner should wait for
the async call to end.
This change introduces a function in the `internals` object that is
intended to be called when the text test execution is completed. The
text test runner will now ignore `on_load_finish` which means a test
will timeout if this new function is never called.
`test(f)` function in `include.js` has been modified to automatically
terminate a test once `load` event is fired on `window`.
new `asyncTest(f)` function has been introduces. `f` receives function
that will terminate a test as a first argument.
Every test is expected to call either `test()` or `asyncTest()` to
complete. If not, it will remain hanging until a timeout occurs.
Although we translate e.g `block` to `block flow` for internal use in
the engine, CSS-DISPLAY-3 tells us to use the short form in
serializations for compatibility reasons.
This adds 9 points to our score on https://html5test.com/ :^)
