$ perl t_inject.pl 
IMPORT(Filter::Inject 0 42) at ../lib/Filter/Inject.pm line 46.
after same line at t_inject.pl line 6.                      <---
--- START MACRO swap at t_inject.pl line 9.
--- END MACRO swap at t_inject.pl line 14.
+1 line at t_inject.pl line 7.
+2 line at t_inject.pl line 8.
42 0 at t_inject.pl line 9.