I think your code doesn't work because it contains errors

I suggest adding:

use strict ;
use warnings ;
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I did a small test myself, see results below:

use strict ;
use warnings ;
use Test::More ;
use Test::Warn;
warning_like ( sub { warn "Hello"; }, qr /Hello/, 'Hello warning' ) ;
done_testing() ;
__END__
ok 1 - Hello warning
1..1
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