pytest conftest confusion

gistfile1.sh

~$ mkvirtualenv myproject
New python executable in myproject/bin/python
Installing setuptools............done.
Installing pip...............done.
virtualenvwrapper.user_scripts creating /opt/env/myproject/bin/predeactivate
virtualenvwrapper.user_scripts creating /opt/env/myproject/bin/postdeactivate
virtualenvwrapper.user_scripts creating /opt/env/myproject/bin/preactivate
virtualenvwrapper.user_scripts creating /opt/env/myproject/bin/postactivate
virtualenvwrapper.user_scripts creating /opt/env/myproject/bin/get_env_details
(myproject)~$ pip install django pytest-django
Downloading/unpacking django
  Downloading Django-1.4.2.tar.gz (7.7Mb): 7.7Mb downloaded
  Running setup.py egg_info for package django
    
Downloading/unpacking pytest-django
  Downloading pytest-django-2.0.0.tar.gz
  Running setup.py egg_info for package pytest-django
    
Downloading/unpacking pytest>=2.3.4 (from pytest-django)
  Downloading pytest-2.3.4.zip (527Kb): 527Kb downloaded
  Running setup.py egg_info for package pytest
    
Downloading/unpacking py>=1.4.12 (from pytest>=2.3.4->pytest-django)
  Downloading py-1.4.12.zip (227Kb): 227Kb downloaded
  Running setup.py egg_info for package py
    
Installing collected packages: django, pytest-django, pytest, py
  Running setup.py install for django
    changing mode of build/scripts-2.7/django-admin.py from 664 to 775
    
    changing mode of /opt/env/myproject/bin/django-admin.py to 775
  Running setup.py install for pytest-django
    
  Running setup.py install for pytest
    
    Installing py.test script to /opt/env/myproject/bin
    Installing py.test-2.7 script to /opt/env/myproject/bin
  Running setup.py install for py
    
Successfully installed django pytest-django pytest py
Cleaning up...
(myproject)~$ django-admin.py startproject myproject
(myproject)~$ cd myproject/
(myproject)~/myproject$ export DJANGO_SETTINGS_MODULE=myproject.settings
(myproject)~/myproject$ py.test
ERROR: Could not import settings 'myproject.settings' (Is it on sys.path?): No module named myproject.settings
(myproject)~/myproject$ touch conftest.py
(myproject)~/myproject$ py.test
========================================== test session starts ==========================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.4
plugins: django
collected 0 items 

===========================================  in 0.01 seconds ============================================
(myproject)~/myproject$ rm conftest*
(myproject)~/myproject$ echo "import pytest
> pytestmark = pytest.mark.django_db
> def test_project(): assert 1
> " > test_project.py
(myproject)~/myproject$ py.test
ERROR: Could not import settings 'myproject.settings' (Is it on sys.path?): No module named myproject.settings
(myproject)~/myproject$ touch conftest.py
(myproject)~/myproject$ py.test
================================================== test session starts ===================================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.4
plugins: django
collected 1 items 

test_project.py .

================================================ 1 passed in 0.29 seconds ================================================
(myproject)~/myproject$ python manage.py startapp myapp
(myproject)~/myproject$ echo "def test_app():assert 1" > myapp/test_app.py
(myproject)~/myproject$ py.test
================================================== test session starts ===================================================
platform linux2 -- Python 2.7.3 -- pytest-2.3.4
plugins: django
collected 2 items 

test_project.py .
myapp/test_app.py .

================================================ 2 passed in 0.21 seconds ================================================
(myproject)~/myproject$ rm conftest*
(myproject)~/myproject$ py.test
ERROR: Could not import settings 'myproject.settings' (Is it on sys.path?): No module named myproject.settings
(myproject)~/myproject$ ls . myapp
.:
итого 56
drwxrwxr-x  5 krya krya  4096 Дек  5 12:23 .
drwxr-xr-x 96 krya krya 32768 Дек  5 12:08 ..
-rw-rw-r--  1 krya krya   252 Дек  5 12:08 manage.py
drwxrwxr-x  3 krya krya  4096 Дек  5 12:22 myapp
drwxrwxr-x  2 krya krya  4096 Дек  5 12:16 myproject
drwxrwxr-x  2 krya krya  4096 Дек  5 12:14 __pycache__
-rw-rw-r--  1 krya krya    79 Дек  5 12:14 test_project.py

myapp:
итого 32
drwxrwxr-x 3 krya krya 4096 Дек  5 12:22 .
drwxrwxr-x 5 krya krya 4096 Дек  5 12:23 ..
-rw-rw-r-- 1 krya krya    0 Дек  5 12:19 __init__.py
-rw-rw-r-- 1 krya krya  125 Дек  5 12:22 __init__.pyc
-rw-rw-r-- 1 krya krya   57 Дек  5 12:19 models.py
drwxrwxr-x 2 krya krya 4096 Дек  5 12:22 __pycache__
-rw-rw-r-- 1 krya krya   24 Дек  5 12:20 test_app.py
-rw-rw-r-- 1 krya krya  383 Дек  5 12:19 tests.py
-rw-rw-r-- 1 krya krya   26 Дек  5 12:19 views.py
(myproject)~/myproject$ cat test_project.py
import pytest
pytestmark = pytest.mark.django_db
def test_project(): assert 1

(myproject)~/myproject$ cat myapp/test_app.py
def test_app():assert 1
(myproject)~/myproject$