How do I solve this error: “Class PHPUnit_Extensions_SeleniumTestCase could not be found”

require_once 'PHPUnit/Extensions/SeleniumTestCase.php';

class WebTest extends PHPUnit_Extensions_SeleniumTestCase
{
    protected function setUp()
    {
        $this->setBrowser('*firefox');
        $this->setBrowserUrl('http://www.example.com/');
    }

    public function testTitle()
    {
        $this->open('http://www.example.com/');
        $this->assertTitleEquals('Example Web Page');
    }
}

/PEAR/PHPUnit/Extensions/SeleniumTestCase.php

pear uninstall phpunit/PHPUnit

pear uninstall phpunit/PHPUnit_Selenium

pear install phpunit/PHPUnit

pear install phpunit/PHPUnit_Selenium

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

class StackTest extends PHPUnit_Framework_TestCase
{
    public function testPushAndPop()
    {
        $stack = array();
        $this->assertEquals(0, count($stack));

        array_push($stack, 'foo');
        $this->assertEquals('foo', $stack[count($stack)-1]);
        $this->assertEquals(1, count($stack));

        $this->assertEquals('foo', array_pop($stack));
        $this->assertEquals(0, count($stack));
    }
}
?>