Fix test failures on Windows.
Fix test failures on Windows.

rouge8/pip,pradyunsg/pip,xavfernandez/pip,rouge8/pip,sbidoul/pip,pfmoore/pip,pypa/pip,xavfernandez/pip,pradyunsg/pip,pypa/pip,pfmoore/pip,sbidoul/pip,xavfernandez/pip,rouge8/pip