Nat Source Address With Pf


I'm trying to configure NAT rule into pf.

pf.conf file:
load anchor "nat.rules" from "/etc/nat.rules"

nat.rules file:
nat log on en0 from any to ->

This rule says every packet to this subnet, the source address is translated to
I run:
sysctl net.inet.ip.forwarding=1
pfctl -e -f /etc/pf.conf

How can I verify the rule is applied?
Is there log file ?