$ cat math.pm
package math;

use strict;
use warnings;

# Perl Cookbook, 2.1. Checking Whether a String Is a Valid Number
# Return 1 if input is a C float, otherwise undef.
sub is_float {
  ($_[0] && $_[0] =~ /^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$
+/)
    ? return 1
    : return;
}

sub addition {
  my $sum;
  my (@mynumbers) = @_;

  for (@mynumbers) {
    die "invalid argument" if !is_float($_);
  }
  for (@mynumbers) {
    $sum += $_;
  }
  return $sum;
}

1;

__END__
$ cat math.t
use strict;
use warnings;

use Test::More qw(no_plan);
use Test::Exception;
use lib qw(.);

BEGIN { use_ok('math'); }

# ------ some negative tests
throws_ok { math::addition(undef); } qr/invalid argument/,
  q{caught invalid argument ok};
throws_ok { math::addition(q{a}); } qr/invalid argument/,
  q{caught invalid argument ok};
throws_ok { math::addition(1, 2, 3, q{-}); } qr/invalid argument/,
  q{caught invalid argument ok};

# ------ some positive tests
cmp_ok(math::addition(1, 2, 3), q{==}, 6, q{Returns 6});
ok(math::is_float(math::addition(1e2, 2.5, 3.14)), q{Returns a float})
+;
cmp_ok(math::addition(1.5, 2.5, 3.5), q{==}, 7.5, q{Returns 7.5});

__END__
$ prove math.t
math....ok
All tests successful.
Files=1, Tests=7,  0 wallclock secs ( 0.04 cusr +  0.01 csys =  0.05 C
+PU)
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