Write tests for the Packaging System

[fgeorges]

More context, from the minutes of the meeting in Prague in Feb. 2015:
https://lists.w3.org/Archives/Public/public-expath/2015Feb/0005.html

Discussing testing of the HTTP Client, the group asked asked how to
write tests for the Packaging System. QT3 cannot be used (at least
not alone). Options are to (1) create a set of test packages, both
valid and non-valid, covering different cases, and (2) write a set of
queries/stylesheets/pipelines using components in those packages (once
again, some will be not valid to test for failures), etc.