py.test can't import my module

I am struggeling getting a python import right. What I want to achieve is to have a module with several source files and a test folder with unit tests.

No matter what I do, I can't get py.test-3 to execute my tests. My directory layout looks like this:

.
├── module
│   ├── __init__.py
│   └── testclass.py
└── tests
    └── test_testclass.py

The __init__.py file looks like this:

__all__ = ['testclass']

The testclass.py file looks like this:

class TestClass(object):

    def __init__(self):
        self.id = 1

And my unit test like this:

import pytest
from module import TestClass

def test_test_class():
    tc = TestClass()
    assert(tc.id==1)

No matter how I call py.test-3 I will end up with a:

E   ImportError: No module named 'module'