Pytest conventions

Standardize tests on pytest and its idioms instead of mixing in unittest-style patterns. Keep the tests/ directory as a plain directory (no __init__.py), and name test modules test_*.py so pytest can auto-discover them. For setup/teardown logic, prefer yield-based fixtures over imperative request.addfinalizer calls, since they keep setup and teardown code together and are easier to read:

@pytest.fixture
def client():
    db_fd, flaskr.app.config['DATABASE'] = tempfile.mkstemp()
    flaskr.app.config['TESTING'] = True
    with flaskr.app.app_context():
        flaskr.init_db()

    yield flaskr.app.test_client()

    os.close(db_fd)
    os.unlink(flaskr.app.config['DATABASE'])

Also configure the test runner (e.g. tox.ini) to forward extra CLI arguments to pytest (py.test []) so contributors can run a subset of tests or pass extra options such as -k or -v locally (tox -epy27 -- -k test_name).