Running py.test will find test files and in the files test functions.

examples/pytest/py.test.out
$ py.test
=========================== test session starts ============================
platform darwin -- Python 2.7.5 -- py-1.4.20 -- pytest-2.5.2
collected 3 items 

test_fibo.py F
test_fibonacci.py F
test_fibonacci_ok.py .

================================= FAILURES =================================
________________________________ test_fibo _________________________________

    def test_fibo():
        assert mymath.fibo(1) == [1]
        assert mymath.fibo(2) == [1, 1]
>       assert mymath.fibo(3) == [1, 1, 2]
E       assert [1, 1, 5] == [1, 1, 2]
E         At index 2 diff: 5 != 2

test_fibo.py:6: AssertionError
______________________________ test_fibonacci ______________________________

    def test_fibonacci():
        assert mymath.fibonacci(1) == 1
        assert mymath.fibonacci(2) == 1
>       assert mymath.fibonacci(3) == 2
E       assert 5 == 2
E        +  where 5 = <function fibonacci at 0x107f90488>(3)
E        +    where <function fibonacci at 0x107f90488> = mymath.fibonacci

test_fibonacci.py:6: AssertionError
==================== 2 failed, 1 passed in 0.04 seconds ====================