Cirrus
CirrocumulusNormally you'd do this with one of the availability tools.
A while ago I was working where the ops used SiteScope to monitor their applications. If we made changes on the BigIP's, the dashboard would be checked before. if it was all green before the change it had to be all-green again afterwards... It was clever enough to test portions of the site, so it could tell you if it was completely down, or just specific bits.
I think HP own sitescope now. I kind of liked it because it ran locally, not a cloud solution. IIRC it was licensed on the number of queries you had configured, and was flexible enough to do pretty much anything.
There are others out there too. Many of them cloud based though.