Add more unit test cases.
Add more unit test cases.

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