If I support both SIF HTTPS and SIF HTTP, what order does the test harness test them in?

The test harness doesn’t so much actively test your agent as observe what your agent does. If you register over HTTP and then send an event over HTTPS, you will pass the “registers over HTTP” test and the “sends event over HTTPS” test. Typically, though, you would run your agent through whatever it does using one protocol or the other then do the same thing over the other protocol.