The bounds checking tests are xfail because the datetime "fast path"
constructor didn't do bounds checking until bpo-29100 was resolved in
CPython commit b67f0967386a9c90411, which was merged for Python 3.6.
This functionality should be simple to backport to earlier versions in a
future commit.
BPO issue:
https://bugs.python.org/issue29100
CPython commit:
b67f096738