How to add tests

Go to tests.js. Follow the current structure. Please only add tests from specs that are reasonably stable. They don't have to be a CR, just not too much in Flux.

• Don't add specs when there are NO implementations of ANYTHING in the spec.
• Don't add tests that already exist, just with different values. E.g. if calc(1px + 2px) is a testcase, adding calc(2px + 2px) won't help.