gistfile1.py

 $ mkdir mypkg tests
 $ touch mypkg/__init__.py
 $ echo 'bar = 1' > mypkg/foo.py
 $ cat > tests/test_a.py
from mypkg.foo import bar
def test_a():
    assert bar == 1
$ py.test
================================================= test session starts ==================================================
platform darwin -- Python 3.3.4 -- py-1.4.20 -- pytest-2.5.2
collected 0 items / 1 errors

======================================================== ERRORS ========================================================
___________________________________________ ERROR collecting tests/test_a.py ___________________________________________
tests/test_a.py:1: in <module>
>   from mypkg.foo import bar
E   ImportError: No module named 'mypkg'
=============================================== 1 error in 0.01 seconds ================================================

$ PYTHONPATH=. py.test
================================================= test session starts ==================================================
platform darwin -- Python 3.3.4 -- py-1.4.20 -- pytest-2.5.2
collected 1 items

tests/test_a.py .

=============================================== 1 passed in 0.01 seconds ===============================================

You forgot touch tests/__init__.py.

I left it out by choice: http://pytest.org/latest/goodpractises.html#choosing-a-test-layout-import-rules

What happens when __init__.py is present is that pytest adds its parent directory to the path, which also makes mypkg importable. This happens during test collection - therefore, mypkg is not importable at setup time, which is the place where Django apps is loaded.