in reply to How do I tell if my code is using JSON::PP or JSON::XS?

You can try comparing some of the operations that give different results in different modules. I showed some of them in my Glasgow talk in 2018.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In Section Seekers of Perl Wisdom