Emit proper error message when tests.sort() failed

[jelmer]

Migrated from Launchpad: https://bugs.launchpad.net/bugs/1243922

Original Reporter: Kui Shi
Date Created: 2013-10-23 21:08:00.469231+00:00
Status on Launchpad: Triaged
Importance: Wishlist

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All test cases are sorted by tests.sort() in testtools/testsuite.py:sorted_tests(). The default sort key is test id, if there is error in test id, TypeError will be raised:
https://bugs.launchpad.net/python-heatclient/+bug/1243096

We'd better emit proper error message for developer to tell what has happened.

There is a pull request discussion here:
#52