There is nothing wrong with testing both brakes separately but, as Chrisbisc says, you should almost always use both bikes together. Your stopping distance will be much greater only using one alone. So if you want to test the ABS system you also need to try with both brakes together to see the actual benefit you would get from it in a real situation.
But if you are testing the ABS, what are you testing it against? You say you thought it would be better, but is your complaint with the ABS system or just the quality of the brakes?
To properly show the effect of ABS on the bike you need to do all the same tests with normal emergency braking, so you can compare the results.
And on just a general video making point, and if it would not get you into any legal trouble, I would use a piece of chalk to mark on the kerb where the bike stops each time. So with each successive test viewers can instantly visually see and compare the different methods of braking
What you may end up with then is a video which not only demonstrates the qualify the ABS on your specific bike, but also demonstrates proper braking making it a useful learning tool.
At the very least, such a video should show why using both brakes together makes such an important difference over using just one of them. If you are using chalk and brake in the order of back, front, then both then each time you will stop shorter of the previous mark making it very clear the braking power of each option.
And, especially with different coloured chalks for ABS and non-ABS braking, it would be interesting to see the difference between the two methods. It should show that having a proper braking technique is better than relying on ABS to save you.
