def find_package_dirs(paths):
    """Find all package directories in given paths"""
    dirs = []
    for importer, modname, ispkg in pkgutil.iter_modules(paths):
        module_loader = importer.find_module(modname)
        if ispkg:
            yield module_loader.filename

# tmpdir is pytest fixture
def test_find_package_dirs(tmpdir):
    tmpdir.mkdir('foo_package').join('__init__.py').write('', mode='w')
    paths_for_search = [str(tmpdir)]

    dirs = find_package_dirs(paths_for_search)
    
    assert len(dirs) == 1
    assert py.path.local(dirs[0]).basename == 'foo_package'