AddClass.php

<?php

namespace Drupal\phpunit_example;


/**
 * A class with features to show how to do unit testing.
 *
 * @ingroup phpunit_example
 */
class AddClass {
    
    /**
     * A simple addition method with validity checking.
     *
     * @param int|float $a
     *   A number to add.
     * @param int|float $b
     *   Another number to add.
     *
     * @return int|float
     *   The sum of $a and $b.
     *
     * @throws \InvalidArgumentException
     *   If either $a or $b is non-numeric, we can't add, so we throw.
     */
    public function add($a, $b) {
        // Check whether the arguments are numeric.
        foreach ([
            $a,
            $b,
        ] as $argument) {
            if (!is_numeric($argument)) {
                throw new \InvalidArgumentException('Arguments must be numeric.');
            }
        }
        return $a + $b;
    }

}