I run a rapid ping and then run
show system statistics icmp
I want to run another ping test but how do I clear out the old stats?
clear interfaces statistics all does not clear out the icmp stats
show system statistics icmp shows the involvement of the Route Processor in handling ICMP. It's a useful capacity planning tool for setting filters to avoid the RP being attacked by ICMP floods. The counter can't be zeroed from the command line as it's really the output of FreeBSD's
netstat -s. Because of this will will go back to zero when a RP is booted and may have a discontinuity when RPs hitlessly change between master and slave.
For what you are trying to do you could set a firewall filter to count the ICMP packets seen at the interface.