Is there a technical reason why tests are not included in boolean expressions?

Maybe because the variables have to be bound before executing the test?

As you mentioned, test conditions allow a fact-binding to be bound before evaluation. My go-to example would be checking the result of an accumulator

Looking at output of clara.rules.inspect... just wondering, when using inspect on a session, what is the difference in the contents of the :condition-matches vs the :insertions. They seem to have pretty much the same information, but granted, I am just using a single rule and single insertion and trying to inspect the output to figure out what inspect can tell me, and how, at the moment...

I believe that the :condition-matches is meant to capture/explain join nodes, where :insertions should contain what facts were inserted and why they were inserted i believe

It looks like :condition-matches will also show the unconditional inserts (like the initial facts loaded to a session)... does that seem right?