gistfile1.txt

<?php

class ExpressionTest extends PHPUnit_Framework_TestCase
{
    /** @test */
    public function it_generates_Number()
    {

        $number = Luhn::make();
        $this->generate('Luhn', $number);

        $number = Luhn::make()->find($number);
        $this->assertTrue($number);

        $number_length = Luhn::make();
        $this->generate('Luhn', $number_length);

        $number_length = Luhn::make()->compare();
        $this->assertEquals($number_length, $number);

        $eachSecond = Luhn::make();
        $this->generate('Luhn', $eachSecond);

        $number = Luhn::make()->find();
        $this->assertTrue($eachSecond);

        $total = Luhn::make();
        $this->generate('Luhn', $total)
            ->find($chislo)
            ->then($total);
        $this->assertTrue($total);

        $this->assertTrue($total);
        $this->assertFalse($total);
    }

}

gistfile2.txt

<?php

class Luhn
{

    public static function make()
    {
        return new static;
    }

    public function luhn_check($number)
    {

        $number = preg_replace('/\D/', '', $number);

        $number_length = strlen($number);
        $eachSecond = $number_length % 2;

        $total = 0;
        for ($i = 0; $i < $number_length; $i++) {
            $chislo = $number[$i];
            if ($i % 2 == $eachSecond) {
                $chislo *= 2;

                if ($chislo > 9) {
                    $chislo -= 9;
                }
            }

            $total += $chislo;
        }

        return ($total % 10 == 0) ? true : false;

    }
}