3) Don't use test_expectations.txt to suppress failures across a
single cycle of the bot, just so you can gather updated baselines
without the tree going red. While it might seem that you're doing tree
maintainers a favor, in my experience this just makes things confusing
and it's better to let the tree go red until you can actually
rebaseline things. It's too easy to add a suppression "for now" and
then forget about it.