Oh, so it's not that your video is black on Twitch, it's that nothing gets to Twitch at all.
That sounds like a different problem, and could be anything in
this thread...
Have you tried lower output resolutions, such as 1280x720 or lower? If those also fail, then it's unlikely Twitch is just rejecting the stream signal.
Have you tried a different Twitch server? If another server also fails, then it's probably not a Twitch problem.
Does any other streaming software work for streaming to Twitch from the same computer and same Internet connection? If not, then likely culprits are your antivirus/firewall software, your router, or your ISP not playing nice. If something else
does work, then the issue could still be your antivirus/firewall.
Regardless of all of this, you should probably reduce your output resolution to 720p@30f at most if you're stuck with 1000 Kbps CBR.
As an aside, the only error that I know of with the Twitch Bandwidth Test is the missing VCRUNTIME140.DLL error.
If you get a missing VCRUNTIME140.DLL error then you need the
VS2015 redistributable (x86).