I had exactly the same thing happen today as well (unrepeatable failure in test_bug453523). Would it defeat the purpose of the test to use a fixed starting point for the random numbers so the results are repeatable?
Yes, it would defeat the purpose. Randomization is there deliberately to minimize dubious assumptions. And this paid off! list.sort() is broken now in a way it wasn't broken in 2.3, and a fixed test case probably would not have revealed this.