python unittest discover

Question

I don't understand something, with the python unittest discover. I made this project:

project/
    __init__.py
    src/
        __init__.py
        criteria.py
    tests/
        __init__.py
        criteria_test.py

And to be able to know if I loaded the test correctly I ensure myself to make it fail with the code below

# coding: utf-8
import unittest

class TestCriteria(unittest.TestCase):
    def setUp(self):
        pass
    def test_criteriaFailure(self):
        self.assertTrue(False)

When I do the command in the command-line, I'm at the file project (the root of my packages), I guess everything can be imported.

I tried:

python -m unittest discover
python -m unittest discover -s tests -p '*_test.py'

but it always return me this output:

Ran 0 tests in 0.000s

Ok

I'd like to understand how to use this feature (I'm using python3.2.3) without having to download and install Nose.