Hi Stefan,
I think the extra predicates you suggest are fine,
feel free to push the changes. I haven't actually
pushed the (skip-unless ... "cargo") commit because
of the ongoing repo issues. If you can push, I invite
you to push that, too.
Maybe also adjust the autopep8 test expectation
to match your result. Or maybe write the reformat
test using something stabler, like "clangd" if you have it.
As for the :expensive, what do you think makes a test
expensive. The longest-running tests in my machine
take less than 3 seconds. But I'm not running the
jtdls one (and I seem to remember that takes a bit
more time). So here, too, fell free to add :expensive
tags to those tests.
João