Add HRM threshold test(s)

[nigelmegitt]

It would be useful to be able to test that processors correctly present subtitles just at the maximum limit of HRM complexity, but I think there are no such tests in this repo for that case right now. If we could add one that would be very helpful. I seem to remember that there are examples from previous work that might be re-usable here - I guess @palemieux could answer this?

[css-meeting-bot]

The Working Group just discussed Add HRM threshold test(s) #37, and agreed to the following resolutions:

• SUMMARY: As discussed in the IMSC spec w3c/imsc#71, we will add HRM threshold and fail tests which are positive tests for validating processors.

The full IRC log of that discussion

<nigel> Topic: Add HRM threshold test(s) #37
<nigel> github: https://github.com//issues/37
<nigel> SUMMARY: As discussed in the IMSC spec w3c/imsc#71, we will add HRM threshold and fail tests which are positive tests for validating processors.