Declare your plan at execution time

use Test::More tests => 6;


use Test::More;
plan tests =>  6;

No need to tell your plan at load time;
Earlier when we were talking about Test::Simple we had a case when the test data was placed in an array and the test script looped over the array executing the function to be tested for each input.
Later we moved the data to an external file which made it even more difficult to declare the plan so we used lengthy code in the BEGIN block in order to have the expected number of tests before Test::Simple is loaded into memory.
With Test::More we have a much better solution. We don't have to declare the plan on the use Test::More line. We can do that later, in the run time of the Perl script.

use strict;
use warnings;

use lib 'lib';
use MyTools;

use Test::More;

my @tests = (
    [ 1, 1, 2 ],
    [ 2, 2, 4 ],
    [ 2, 2, 2, 6],
    [3, 3, 6],
    [-1, -1, -2],
    [1, -1, 0],

plan tests => scalar @tests;

foreach my $t (@tests) {
    my $expected = pop @$t;
    my $real     = sum(@$t);
    my $name     = join " + ", @$t;

    ok( $real == $expected, $name );