assert that an operation raises a Stopiteration

Question

I have a generator that I want to confirm has ended (at a certain point in the program. I am using unittest in python 2.7

# it is a generator whould have only one item
item = it.next()
# any further next() calls should raise StopIteration
self.assertRaises(StopIteration, it.next())

But it fails with the message

======================================================================
ERROR: test_productspider_parse_method (__main__.TestMyMethods)
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Traceback (most recent call last):
  File "/home/myName/tests/__main__.py", line 94, in test_my_method
    self.assertRaises(StopIteration, it.next())
StopIteration

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Answer 1

You need to pass the method itself instead of calling the method. In other word, drop the parentheses.

self.assertRaises(StopIteration, it.next)

Or you can use it as a context manager:

with self.assertRaises(StopIteration):
    it.next()