JRahm mentioned QKView analysis and that is actually an excellent way to check for iRule issues. During the QKView review process, logs are actually trolled to see if there were any iRule execution errors. You can do the same manually in real-time by tailing /var/log/ltm as well. In older versions of BIG-IP the QKView review in iHealth would also alert you to any changes in namespaces and methods in newer code releases. Finally, you can also program against the iHealth API easily using Python or Postman. I have done this to obtain a list of CVEs for example on my current version of BIG-IP. You could simply upload the QKView quarterly, and parse the results for any hits on keywords like "irule" for instance in the returned JSON.