正则表达式和PHPUnit断言：计算重复模式中单词匹配的次数

I'm using PHPUnit to test the output of a PHP function that produces HTML option tags using provided data.

For example, this is a correct output of the function (I added line returns to improve readability on SO):

<option value="0">Choose one ...</option>
<option value="fooID">fooValue</option>
<option value="barID"selected>barValue</option>
<option value="bazID">bazValue</option>

And to test the output, I'm using this assertion:

$this->assertRegExp("/(<option value=\".*\" *(selected)? *>.*<\/option>)+/i", $res);

where $res is the output string of the tested function.

And it works well. But I would like to also check that selected is generated in only one option tag.

How can I do this? Is there a way to count how many times selected was matched?

Thanks in advance, be kind, it's my first question on SO :-)

Don't use regexes to parse HTML or XML documents. Use a DOM parser:

// create a document object from the HTML string
$doc = new DOMDocument();
$doc->loadHTML($html);

// create a XPath selector
$selector = new DOMXPath($doc);

// select nodes containing the selected attribute
$result = $selector->query('//*[@selected]');

// make assertion
$this->assertEquals(1, $result->length, 'Failed to assert that result contains exactly one selected element');