Contact: css21testsuite-submissions (at) gtalbot [dot] org
If your testcase does not comply with such guidelines or such format, I will help and assist you.
Testcases already submitted to CSS 2.1 test suite by various parties
If you want to be credited for the testcases you submit, then you will have to eventually sign up the W3C's license grant form so that you W3C permission to distribute your contributions. Read more info on How to License Your Contribution. I will assist you if you need help on this issue.
Yes, absolutely! A testcase which is passed by all current mainstream browsers is less helpful, less useful for all mainstream browser development teams than one that is failed by 1 or a few browser manufacturers. The number 1 purpose of a CSS test suite is to help achieve interoperable implementations of CSS 2.1 among web browsers and web-capable softwares. So, identifying tests which are not properly supported or which are not correctly implemented in the latest stable version of a mainstream browser is helpful and relevant. A failure in a particular test will inform the involved browser manufacturer development team about it.
There are many positive aspects to submitting testcases which fail in recently released specific browser versions (e.g. Internet Explorer 8, Firefox 3.5.7, Opera 10.10, Safari 4.0.4, Chrome 18.104.22.168, Konqueror 4.3.4, etc). Still today, I would say that 66% of all questions asked in web authoring forum discussions newsgroups or in BBS are about browser incompatibilites (or suspected browser bugs) when rendering a particular webpage (markup and CSS) code.
Ideally, the best opportune moment to sign up that form would be when you have submitted all of the testcases which you wanted to submit.