Your benchmark is meaningless because @nums is not in scope when the benchmarked code is executed. That's because it's a my variable and has lexical scope; when the code is executed in a different scope (package Benchmark), @nums is no longer in scope. So you're doing your tests on an empty array.

Instead of a my var you should use use vars.

When I run your test having done that I get this:

Benchmark: running Do_not_test, Test_defined, each for at least 10 CPU
+ seconds...
Do_not_test: 10 wallclock secs (10.18 usr +  0.00 sys = 10.18 CPU) @ 7
+98.13/s (n=8125)
Test_defined: 10 wallclock secs (10.16 usr +  0.00 sys = 10.16 CPU) @ 
+671.75/s (n=6825)
[download]

So there is a difference.