sub warns (&) {
	my $sub = shift;
	my @warns;
	{ local $SIG{__WARN__} = sub { push @warns, shift };
		$sub->() }
	return wantarray ? @warns : scalar @warns;
}

##</code><code>##

sub some_module_code {
	my $arg = shift;
	warn "Some custom warning about $arg";
}

my @w = warns {
	some_module_code("foo");
};
is grep({/\bSome custom warning\b/i} @w), 1;
is grep({/\bUse of uninitialized value\b/i} @w), 0;