Calculator.php

<?php

namespace Acme\Calculator;

class Calculator
{
    public $a;
    public $b;

    public function __construct($a, $b)
    {
        $this->a = $a;
        $this->b = $b;
    }

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

// ====================================================================================================================

    public function getA()
    {
        return $this->a;
    }

    public function getB()
    {
        return $this->b;
    }

    public function uglyAdd()
    {
         return $this->getA() + $this->getB();
    }

// ====================================================================================================================

    protected function hiddenAdd($a, $b)
    {
        return $a + $b;
    }

}

CalculatorTest.php

<?php

namespace Acme\Tests;

class CalculatorTest extends \PHPUnit_Framework_TestCase
{
    public function calcData()
    {
        return array(
            array(array(1, 3), 4),
            array(array(5, 5), 10),
            array(array(3, 9), 12),
            array(array(4, 3), 7),
            array(array(0, -1), -1),
        );
    }

    public function mockObjectWipeAllMethodsAndAlwaysWillReturnNullWithout_SET_METHODS_Call()
    {
        $caclMock = $this->getMockBuilder('Acme\Calculator\Calculator')
            ->disableOriginalConstructor()
            // uncomment and tune me, pleeease
            // ->setMethods(null)
            ->getMock()
        ;

        $this->assertEquals(null, $caclMock->add(1, 2));
    }

    /**
     * @dataProvider calcData
     */
    public function testCalcAddMethod($data, $result)
    {
        $caclMock = $this->getMockBuilder('Acme\Calculator\Calculator')
            ->disableOriginalConstructor()
            ->setMethods(null)
            ->getMock()
        ;

        $this->assertEquals($result, $caclMock->add($data[0], $data[1]));
    }

    /**
     * @dataProvider calcData
     */
    public function testCalcUglyAddMethod($data, $result)
    {
        $caclMock = $this->getMockBuilder('Acme\Calculator\Calculator')
            ->disableOriginalConstructor()
            ->setMethods(array('getA', 'getB'))
            ->getMock()
        ;

        $caclMock->expects($this->any())->method('getA')->will($this->returnValue($data[0]));
        $caclMock->expects($this->any())->method('getB')->will($this->returnValue($data[1]));

        $this->assertEquals($result, $caclMock->uglyAdd());
    }

    /**
     * @dataProvider calcData
     */
    public function testCalcHiddenAddMethod($data, $result)
    {
        $caclMock = $this->getMockBuilder('Acme\Calculator\Calculator')
            ->disableOriginalConstructor()
            ->setMethods(null)
            ->getMock()
        ;

        $reflMethod = new \ReflectionMethod($caclMock, 'hiddenAdd');
        $reflMethod->setAccessible(true);

        $this->assertEquals($result, $reflMethod->invokeArgs($caclMock, array($data[0], $data[1])));
    }

}

We don't need use setMethods() at testCalcHiddenAddMethod because we use a Reflection.