I agree, but we can get a bit closer.

It offers a bit more control (for individual tests) about the parsing environment (And more of these can be added). I was also thinking we could have one that would expect the file to be finished in below N calls to webvtt_parse_chunk, and other failure criteria like that. Of course this wouldn't really help in the case of endless loops, so a timeout feature is needed there, which should be doable with the C++ bindings, but we don't have it implemented anywhere currently.