Although it may not be what you were looking for, don't forget that a Servlet is still a Java class. You can put a "main" method in it and call any methods that you want, as long as you can give it the right parameters.
I sometimes use this approach if I need to prform ad-hoc tests of some of the code in a Servlet. It's just a shame how the creators of the Servlet API made it so difficult to "mock" the Request and Response objects.
If you find yourself with methods in a servlet class that need to be tested from a command line, you should take that as a indication that it might be a good idea to refactor the class. If you can create one or more "helper" classes that can be tested outside the servlet environment, it speeds up development and testing.