For that test I fairly easily heard 22 kHz. I also tried the aliasing test, and my system passed. Testing myself with tones I generated with Audacity, I was able to hear up to 23 kHz, but nothing past that. At that point, I'm not sure if it's my ears or my equipment that's causing the roll-off. I'll just assume it's my ears.
Any sine wave above 15 kHz is brutal. Those are some really painful tones to listen to!!
BTW, aliasing works like this:
Let's say you have two sine waves: one at 2 kHz and the other at 4 kHz. The one at 4 kHz can sound exactly the same as the 2 kHz tone if aliasing is present. It's a bit hard to describe, but maybe this image will help.
Notice that there are two sine waves present, the red one and the blue one. Each have the exact same values where the dots are located. When you sample an analog signal to turn it into a digital signal, all you really are doing is taking several of these "dots" and using them to represent your original signal. Unfortunately, in doing this, two different signals can look identical. This is known as aliasing; one frequency appears exactly the same as another one. In this case, the blue sine wave is sampled correctly while the red one is sampled incorrectly. The red one will sound like the blue one.
The sampling rate for a CD is 44.1 kHz, which basically means that anything under 22.05 kHz will be sampled correctly, and anything above that will be aliased to another frequency below 22.05 kHz. This won't be a problem in audio recordings because anti-aliasing filters are used in order to basically attenuate anything above 22.05 kHz from the original signal.
If you heard a rising tone instead of a falling tone during the aliasing test, it means that your system is experiencing aliasing. For this test, a system that experiences aliasing will be representing higher frequencies as lower ones, and vice-versa.