defined &{$TEST->test_sub}

This would actually (try to) call the method...

#!/usr/bin/perl

my $TEST = "foo";
if ( defined &{$TEST->test_sub} ) { }

__END__
Can't locate object method "test_sub" via package "foo" (perhaps you f
+orgot to load "foo"?) at ./798474.pl line 4.

---

#!/usr/bin/perl

my $TEST = "foo";
if ( defined &{$TEST->test_sub} ) { }

package foo;

sub test_sub { print "hi\n" }
__END__
hi
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