gistfile1.txt

(0)hpk@teta:~/p/pytest$ cat test_x.py 

def test_assert():
    x = 3
    assert x == 4

(0)hpk@teta:~/p/pytest$ python -OO -m pytest test_x.py 
WARNING: assertions which are not in test modules will be ignored because assert statements are not executed by the underlying Python interpreter (are you using python -O?)
============================= test session starts ==============================
platform linux2 -- Python 2.7.3 -- pytest-2.4.3.dev2
plugins: xdist, cov, pep8, xprocess, capturelog, yamlsound, localserver, cache, flakes, instafail, timeout
collected 1 items 

test_x.py F

=================================== FAILURES ===================================
_________________________________ test_assert __________________________________

    def test_assert():
        x = 3
>       assert x == 4
E       assert 3 == 4

test_x.py:5: AssertionError
=========================== 1 failed in 0.03 seconds ==========================