Testing Extension Upgrade Paths

Hello -

I understand how to setup a regression suite for a postgres extension, but
what I'm not clear on from the docs is if there is a pattern that exists
for testing not only the latest version of an extension, but also an
upgraded previous version.

For example, I am developing version 1.1, and the test suite runs fine for
1.1.

But I want to install the extension at 1.0, do a few things, then upgrade
to 1.1 and run N tests over again from this path.

I have in mind something like an environment variable or something where
you could run the suite twice with the variation being a direct install at
the highest version, or an upgrade from a previous version. Please excuse
my ignorance!

Is there any straightforward way to do this that doesn't involve manually
copying tests?

Thank you!
Jeremy

P.S. is this the right list for extension dev questions ???