Thank you for the sig tip, xpi0t0s. You can do the trial test there.
The site is commercial, developed by myself. The tests, including the C test, have been put together by a group of talented individuals and we now need beta testers to validate the C test before it is used in anger.
If you would like to see how good is your C, contact me with your email and I will get you the set of credentials to do the test.
I hope this helps.