<?php
// [...] //

function mockGetNumber($number) {
   return $number;
}

function testPHUnitCandDecideByParameter() {
   $someObject = new SomeClass();
   // With PHPUnit
   $phpunitMock = $this->getMock('AClassToBeMocked');
   $phpunitMock->expects($this->any())->method('getNumber')->will($this->returnCallback(array($this, 'mockGetNumber')));
   $this->assertEquals(4, $someObject->doubleNumber($phpunitMock, 2));
   $this->assertEquals(6, $someObject->doubleNumber($phpunitMock, 3));
}

class AClassToBeMocked {
// [...] //
   function getNumber($number) {
      return $number;
   }
}

class SomeClass {
   // [...] //
   function doubleNumber($anotherObject, $number) {
      return $anotherObject->getNumber($number) * 2;
   }
}