Ecertifications.com offers two levels of Cold Fusion certificate: regular and Master level. To pass on the Master level you must get 75% of the questions correct. To get a regular certificate, you need 60% right. Most of the questions are directly related to the ColdFusion programming language itself. They also ask a couple of questions related to Bright Tiger and regarding the way ColdFusion works in a Linux/Unix environment.
For a complete listing of topics on this test, see http://www.ecertifications.com/cert/coldfusion.html.
Don't worry if you don't get a Master's level certificate the first time you take the exam. Ecertifications.com is free and you can take the tests as many times as you like via the internet. If you pass, they send you a certificate and allow you to use their logo on your resume. The ColdFusion test is about 50 questions and really pretty good overall. Passing it definitely shows you know something and in the absence of other methods of benchmarking your ColdFusion abilities, this is definitely a good start.
Ecertifications.com also offers certificates in other areas as well. For instance, they have SQL Server administrator, C++ programmer, XML Programmer and many more.
If you are interested in this kind of testing, you'll also want to know about Brainbench.Com. Similar to ecertifications.com, Arlington, Virginia-based Brainbench.com (formerly Tekmetrics) has even more tests available and they have a better testing interface. Unfortunately, they don't have a ColdFusion test yet, but I am told they are working on one now. Brainbench takes the certifications a step further by giving you the choice to be listed for potential employers.
P.S. I hear Allaire is starting a certification of their own in the Fall.