关于单元测试：在Python unittest中，SystemExit：False打印即使测试运行“OK”

In Python unittest, SystemExit: False printed even though the test ran “OK”

我正在写一个类RecurringInterval，它应该代表周期性的间隔，并首先尝试按如下方式测试它：

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import datetime
import dateutil.relativedelta
import dateutil.rrule
import dateutil.parser

class RecurringInterval(object):
def __init__(self, *args, **kwargs):
self.period = kwargs.pop('period', None)
assert isinstance(self.period, datetime.timedelta) or isinstance(self.period, dateutil.relativedelta.relativedelta) or (self.period is None)
self.rrule = dateutil.rrule.rrule(*args, **kwargs)

def __contains__(self, time):
last_occurrence = self.rrule.before(time)
return (last_occurrence <= time) and (time <= last_occurrence + self.period)

if __name__ =="__main__":
start = dateutil.parser.parse("Thu Nov 24 14:00 UTC 2016")
recurring_interval = RecurringInterval(dateutil.rrule.DAILY, dtstart=start, count=5, period=datetime.timedelta(hours=2))
time = dateutil.parser.parse("Thu Nov 24 15:00 UTC 2016")
print(time in recurring_interval)

运行时，该程序按预期打印True。

接下来，我想将此脚本转换为unittest。我对代码进行了以下调整：

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import datetime
import dateutil.relativedelta
import dateutil.rrule
import dateutil.parser
import unittest

class RecurringInterval(object):
def __init__(self, *args, **kwargs):
self.period = kwargs.pop('period', None)
assert isinstance(self.period, datetime.timedelta) or isinstance(self.period, dateutil.relativedelta.relativedelta) or (self.period is None)
self.rrule = dateutil.rrule.rrule(*args, **kwargs)

def __contains__(self, time):
last_occurrence = self.rrule.before(time)
return (last_occurrence <= time) and (time <= last_occurrence + self.period)

class TestRecurringInterval(unittest.TestCase):
def test_contains_method_for_primary_interval(self):
start = dateutil.parser.parse("Thu Nov 24 14:00 UTC 2016")
recurring_interval = RecurringInterval(dateutil.rrule.DAILY, dtstart=start, period=datetime.timedelta(hours=2))
time = dateutil.parser.parse("Thu Nov 25 15:00 UTC 2016")
self.assertTrue(time in recurring_interval)

if __name__ =="__main__":
unittest.main()

但是，当我运行它时，我得到一个例外：

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In [24]: exec(open('recurring_interval.py').read())
.
----------------------------------------------------------------------
Ran 1 test in 0.002s

OK
An exception has occurred, use %tb to see the full traceback.

SystemExit: False

/usr/local/lib/python3.5/dist-packages/IPython/core/interactiveshell.py:2889: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)

回溯内容如下：

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In [25]: %tb
---------------------------------------------------------------------------
SystemExit Traceback (most recent call last)
<ipython-input-24-ab8976376637> in <module>()
----> 1 exec(open('recurring_interval.py').read())

<string> in <module>()

/usr/lib/python3.5/unittest/main.py in __init__(self, module, defaultTest, argv, testRunner, testLoader, exit, verbosity, failfast, catchbreak, buffer, warnings, tb_locals)
92 self.progName = os.path.basename(argv[0])
93 self.parseArgs(argv)
---> 94 self.runTests()
95
96 def usageExit(self, msg=None):

/usr/lib/python3.5/unittest/main.py in runTests(self)
255 self.result = testRunner.run(self.test)
256 if self.exit:
--> 257 sys.exit(not self.result.wasSuccessful())
258
259 main = TestProgram

SystemExit: False

导致此异常的原因是什么？测试未成功运行吗？