A %% needs to be added before the first line. Otherwise, the server parses that first line of the test suite as a comment. I've fixed it here; feel free to fix this problem wherever else it occurs in problems you've created.

@goc3 that broke my test! Seems there is some implicit scoping rule, by adding the %% it means that T is not available in subsequent %% cells. Fixed it by calling the user function multiple times. This stuff is not well documented: the scoping rules, the need for a leading %% etc.

Sorry for any confusion that may have been caused. Yes, there may be a need for more detailed explanations of some site functioning, but that is beyond my power. For what it's worth, the scoping rule is consistently applied for all problems on the site: variables called within each test case are only available to that test case. I (and many other problem creators) end up repeating lines for any required variables within each test case.