Se api

Just for preview. Please don't merge it.
Hi SY,
I guess we're testing low level stuff and corner cases that can't be easily tested from a user TA. When this feature is completed we're mostly interested in seeing that all tests passes. From xtest point of view it's OK with a single test case that can either pass or fail since we're mostly interested in seeing whether we have a regression or not. Xtest isn't a debug tool. It helps highlighting regressions and can help reproducing problems, debugging is done by other means (gdb, printfs or whatever).