add in a test framework similar to pip

[qwcode]

add in a test framework similar to pip.

• pytest for the sake of the easy tmpdir support
• a fixture for scripttest functional test environments

without this, it's hard to ask/get people to add tests for changes.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Just add a comment if you want to keep it open. Thank you for your contributions.