calc.php

<?php namespace App;

class Calc
{
    public function add($a, $b)
    {
        return $a + $b;
    }

}

calcTest.php

<?php

require 'app/calc.php';
use App\Calc;

class CalculatorTest extends PHPUnit_Framework_TestCase
{

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

    public function testAdd()
    {
        $this->assertEquals(3, $this->calc->add(1, 2));
    }

}