Could you use the assert method which also takes the description string (maybe including the relevant date and/or offset into the message). Unfortunately, when it comes to the test for the constraint validators we were a bit sloppy with using just assertTrue(condition), but if you look at the rest of the test, you will notice that we usually always provide a message. It just really helps when a test actually fails. In particular the loop makes things tricky, since if a test fails, there is no telling in which iteration it does so, until you start debugging. 

The test is much better now though :-)