学习《Dive Into Python3》 Python 单元测试问题

http://www.diveintopython3.net/unit-testing.html 中 9.2 A Single Question 中执行 python3 romantest1.py -v 会出现以下详细的信息

test_to_roman_known_values (__main__.KnownValues) ①
to_roman should give known result with known input ... FAIL ②

======================================================================
FAIL: to_roman should give known result with known input
----------------------------------------------------------------------
Traceback (most recent call last):
File "romantest1.py", line 73, in test_to_roman_known_values
self.assertEqual(numeral, result)
AssertionError: 'I' != None ③

----------------------------------------------------------------------
Ran 1 test in 0.016s ④

FAILED (failures=1) ⑤

但是我自己在 windows 7 系统 python3.5.2 环境下执行 python romantest1.py -v，只输出

PS E:\DiveIntoPython3> python .\romantest1.py -v

----------------------------------------------------------------------
Ran 0 tests in 0.000s

OK


代码与连接中的完全相同，不知道哪里出了问题，各位有遇到过的？或者知道是哪里的问题？