Moodle Quiz Engine - assertTag issues a warning if tag is not found

Hi,

As I am currently developing a new question type, I just stumble upon a small issue that if corrected will be helpful for developers.

The issue is in base_testcase.php (https://github.com/moodle/moodle/blob/master/lib/phpunit/classes/base_testcase.php#L58)

If $tags is false, i.e. we don't find the node, then count($tags) results in an error. Preventing the following assertion to display the origin of the issue.

If we write instead something like:

$matched = ($tags && count($tags)) && $tags[0] instanceof DOMNode;

It then does not raise an exception and we can see the full assertion message. Seem that it is still the case on Moodle 4.0.