t/op/subst_amp.t See if $&-related substitution works
t/op/substr.t See if substr works
t/op/subst.t See if substitution works
+t/op/substT.t See if substitution works with -T
t/op/subst_wamp.t See if substitution works with $& present
t/op/sub.t See if subroutines work
t/op/switch.t See if switches (given/when) work