This opens the door for replacing all `library ...` lines in toolchain
test files with `library "[[@TEST_NAME]]";`. That's technically more
typing in a lot of cases, but OTOH means we can just do some copy-paste
boilerplate and stop carefully writing library names.
Also cleans up the test setup, because it's getting messy. I'm trying to
make it easier to see the divisions of tests and the output associated
with them. StringSwitch looked like a way to do this, with a few edits
to make it work nicely.
