[Python] How to assert output with nosetest/unittest in python?

I'm writing tests for a function like next one:

def foo():
print 'hello world!'


So when I want to test this function the code will be like this:

import sys
from foomodule import foo
def test_foo():
foo()
output = sys.stdout.getline().strip() # because stdout is an StringIO instance
assert output == 'hello world!'


But if I run nosetests with -s parameter the test crashes. How can I catch the output with unittest or nose module?

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