I haven't seen any fire testing, but I have seen them in a fire. I had a fire at a project under construction a few years ago. It was a wood framed apartment building with CPVC piping. The sprinklers were installed, and most systems were live. The first floor had drywall, and the caps had been removed from the sprinklers. The 2nd floor had drywall, but the caps were still on the sprinklers. The 3rd floor was partially drywalled, and the 4th floor had no drywall, with caps on all the sprinklers.
On the 1st floor, there was very little damage. On the 2nd floor, if the fire reached the sprinkler, the cap popped off and there wasn't much more damage than on the 1st floor. On the 3rd floor, the caps popped off if there was drywall. Without drywall, about half of the caps popped off. On the 4th floor, most of the caps didn't come off, but we think that the fire burned through the supply main near the riser first, so there was no water pressure by the time the fire reach most of the sprinklers.
There was a lot of charred piping, but not much was burned through. The heads where the cap didn't come off all had a red bulb of melted plastic around the head.