Code review comment for lp:~jml/launchpad/buildd-slavescanner-bustage

Thanks for the work on this. We discussed many superficial changes on IRC, and you've made corresponding improvements: separate creation of complex expected values from comparisons to actual values. Better not import twisted.trial.unittest under that name since it leads to confusion with the global unittest. Use a list comprehension instead of a loop calling a function. Use transaction instead of layer.txn. Bear our syntax guidelines in mind when initializing dicts.

Discussed but not changed:
 * Testing the logic without Twisted. Complete the overhaul first, then be clever.
 * Extracting more of the unit test setup into helpers to make the tests shorter. First see what parameterization would be needed as the tests grow.