Add in some tests

[whikloj]

I'm not going to go crazy here, but I need tests to see how things are meant to operate so I figured if I was writing them, you might want them. But you can close this too.

CAUTION if you do want these tests then please be aware that the composer.lock and the test structure only goes to PHP 7.3 as I no longer have access to a 7.2 instance to update the lock file.

So if you want to support 7.2, you would need to

1. Using PHP 7.2 run composer update
2. Add that updated composer.lock to this PR
3. Add "7.2" as one of the php-versions in the ci_workflow.yml below. (line 24)

Also this duplicates some of the changes in #81