Testing Private Methods Not Working

Here is my Test Class;

<?php
namespace stats\Test;

use stats\Baseball;

class BaseballTest extends \PHPUnit_Framework_TestCase
{

  public function setUp() {
    $this->instance = new Baseball();
  }

  public function tearDown() {
    unset($this->instance);
  }

  public function testOps() {
    $obp = .363;
    $slg = .469;
    $ops = $this->instance->calc_ops($obp, $slg); //line 23

    $expectedops = $obp + $slg;

    $this->assertEquals($expectedops, $ops);
  }

}

And this is my Baseball Class;

<?php
namespace stats;

class Baseball
{
  private function calc_ops($slg,$obp)
  {
   return $slg + $obp;
  }
}

And I keep getting this error when I run my tests;

Fatal error: Call to private method stats\Baseball::calc_ops() from context 'stats\Test\BaseballTest' in /media/sf_sandbox/phpunit/stats/Test/BaseballTest.php on line 23

This is only a tutorial I am following.. But it's not working so it's frustrating because I am following it exactly.