ASA 5512-X: How to verify the firewall fails closed if the filtering function becomes nonfunctional?

[Intelligentemphasis]

This firewall does not have FirePower or any other services. It is just the ASA itself. 

I need to verify some security requirements and I can't find cisco documentation that states if this is a default configuration or how to change/verify it myself.

[gerald.scott]

What are you referring to when you say "filtering function"?  If you're referring to traffic not matching an ACL, that traffic will be dropped, which I guess you could say it fails closed.  If you're referring to the ASA itself failing, then that is definitely closed as the device won't be passing traffic at that point.