Calc.php

<?php
class Calc
{
    public function add($a, $b, $c = NULL)
    {
        if (isset($c)) {
            return $a + $b + $c;
        } else {
            return $a + $b;
        }
    }
}

Calc_02.php

<?php
class Calc
{
    public function add()
    {
        $num = 0;
        $cnt = func_num_args();
        for ($i = 0; $i < $cnt; $i++) {
            $num += func_get_arg($i);
        }
        return $num;
    }
}

CalcTest.php

<?php
require_once 'PHPUnit/Framework.php';
require_once './Calc.php';

class CalcTest extends PHPUnit_Framework_TestCase
{
    public function testAdd()
    {
        $calc = new Calc;
        $this->assertEquals(2, $calc->add(1, 1));
    }

    public function testAddThreeNumbers()
    {
        $calc = new Calc;
        $this->assertEquals(3, $calc->add(1, 1, 1));
    }
}

CalcTest_02.php

<?php
require_once 'PHPUnit/Framework.php';
require_once './Calc.php';

class CalcTest extends PHPUnit_Framework_TestCase
{
    protected $calc;

    public function setUp()
    {   
        $this->calc = new Calc;
    }   

    public function testAdd()
    {   
        $this->assertEquals(2, $this->calc->add(1, 1));
    }   

    public function testAddThreeNumbers()
    {   
        $this->assertEquals(3, $this->calc->add(1, 1, 1));
    }   
}

CalcTest_03.php

<?php
require_once 'PHPUnit/Framework.php';
require_once './Calc.php';

class CalcTest extends PHPUnit_Framework_TestCase
{
    protected $calc;

    public function setUp()
    {
        $this->calc = new Calc;
    }

    public function testAdd()
    {
        $this->assertEquals(2, $this->calc->add(1, 1));
    }

    public function testAddThreeNumbers()
    {
        $this->assertEquals(3, $this->calc->add(1, 1, 1));
    }

    public function testAddTenNumbers()
    {
        $this->assertEquals(55, $this->calc->add(1, 2, 3, 4, 5, 6, 7, 8, 9, 10));
    }
}