It's really nice to see everything working but there will be times when you encounter a problem. For example that certain text is missing from the web page:

examples/php/simpletest/web04.php
<?php

require_once(dirname(__FILE__) . '/../../../tools/simpletest/autorun.php');
require_once(dirname(__FILE__) . '/../../../tools/simpletest/web_tester.php');


class TestOfCalculator extends WebTestCase {
    function testBasicCalc() {
        $url = 'http://localhost:8081/php/calc/basic_calc.php';
        $this->assertTrue($this->get($url));
        $this->assertText('Basic Calculator');
        $this->assertTitle('Scientific Calculator');

        $this->assertText('Real Calculator');
    }
}


?>

Will fail with the following output

examples/php/simpletest/web04.txt
web04.php
Fail: TestOfCalculator -> testBasicCalc -> Text [Real Calculator] not detected in
  [String: Scientific Calculator Basic Calculator Value: Value:]
     at [.../examples/php/simpletest/web04.php line 14]
1/1 test cases complete: 3 passes, 1 fails and 0 exceptions.