unittest failed in Windows caused by pytest.fixture

[robberphex]

I run unittest for pip(1.5.4) in Windows 7(64) Python 3.4(64). But unittest is failed:
Run:py.test tests\functional\test_help.py
Exception:TypeError: object of type 'LocalPath' has no len() in \test\lib\ntpath.py:108

It is coused by function join received arg with type LocalPath.

I cannot find what wrong, so report this issue.