use MyExists qw(my_exists);

my %hash = ( 'test1' => 'value1', 'test2' => 'value2' );

print "Real exists: ";
print exists( $hash{'test1'} );
print "\n";

print "My exists: ";
print my_exists( $hash{'test1'} );
print "\n";

print "Real exists: ";
print exists( $hash{'test3'} );
print "\n";

print "My exists: ";
print my_exists( $hash{'test3'} );
print "\n";