Sure. Here you go.
It’s very basic. You press a key and release it. As soon as the key is down, the square in the middle of the screen toggles its color between black and cyan and a short beep (more of a click) is played. If you keep holding the key down, the color toggle/click will happen continuously at a regular rate. The latter is useful for evaluating a lag between the video and audio.
I do, of course. Since I was on the team who discovered, analyzed, and booked down the floating bus on the +2A/+3, I made quite a few tests. Mark Woodmass was the first to implement it in his SpecEmu, and I made a special version of my test for him to fine-tune his emulation. You can check out the link in my signature for the most detailed information about it you can ever find. Here are the links to my test programs:
1. Floating Bus Test (Universal) 2 There are two versions here—2.0 and 2.1. Version 2 is meant to test the best-case scenario. When you launch it, two yellow stripes in the border will appear at the same height as the “ground” level. They may jitter a little bit, but at no point should they appear below or above the yellow ground area. When you press a key, white vertical lines will appear in the “sky” area. Again, the two yellow stripes should remain in the border at the same position and nowhere else on the screen. Pressing and holding a key will cause a single yellow stripe to roll inside the ground area. You can now press and hold keys randomly and the yellow stripe should never appear anywhere else on the screen. Version 2.1 is a preliminary worse-case scenario test. Its only difference from 2.0 is that after pressing a key, the border should fill up with yellow stripes from top to bottom. Holding a key down, will cause a single flickering yellow stripe to roll down across the screen.
2. Woody’s Special. This is the ultimate emulator test. Upon loading, it behaves just like the above. However, after you press a key, it displays a very specific pattern, which is easier to understand by looking at it, rather than reading its description. I ran this test on a real Spectrum +2A and took a video of the screen at 50 fps. You can examine it frame by frame and then fine-tune your emulator to make sure that each frame matches real hardware exactly. The yellow stripes have distinct edges that contrast well with the black border and the white vertical lines should help you see at which exact T state it happens.
(I really should do a writeup on all so I can refer any emulator author to it. The one I did was aimed more at Spectrum software developers.)