How can I test my 100 - 400 L IS to see how good a copy it is

I really do think that my copy of the 100 - 400 isnt the best but also not the worst. I want to conduct a test so I will know wether or not its worth sending it away.

The issue for most people with that lens is how it performs at 400 wide open. Take some pix at that setting and study them.

The "Trombone" as I call it is not the sharpest lens at 400mm, but still sharper than most consumer zooms. I shoot with it wide open most times and use it at 400mm a lot.
It's never gonna be like a prime lens, but still provides L quality sharpness, contrast and color retention. Remember to do the test shots from a tripod with iS off. I do most of my shooting hand-held, so I know the results will vary, depending on situation and light.
You can also post some un-edited images with EXIFF + a 100% crop, so we can tell if it's good or not.

John