use strict;
use warnings;
use Test::More;

use Scalar::Util qw(looks_like_number);

my $x = 42;
my $y = 'not a number';

cmp_ok(looks_like_number(\$x), '==', isNumber(\$x), 'agrees re ref to number');
cmp_ok(looks_like_number(\$y), '==', isNumber(\$y), 'agrees re ref to non-number');

done_testing();

sub isNumber
{
  defined $_[0] or return 0;
  my $R = 1;
  local $SIG{__WARN__} = sub { $R = 0; };
  return ($_[0] < 0) ? $R : $R;
}

__END__

Outputs:

not ok 1 - agrees re ref to number
#   Failed test 'agrees re ref to number'
#   at IsNumber.pl line 10.
#          got:
#     expected: 1
not ok 2 - agrees re ref to non-number
#   Failed test 'agrees re ref to non-number'
#   at IsNumber.pl line 11.
#          got:
#     expected: 1
1..2
# Looks like you failed 2 tests of 2.