Test the select and course elements

testselect.php

<?php
require_once(__DIR__ . '/config.php');
require_once($CFG->libdir.'/formslib.php');
require_login();
$PAGE->set_url(new moodle_url('/testselect.php'));
$PAGE->set_context(context_system::instance());

class testform extends moodleform {
    public function definition()
    {
        global $DB;

        $this->_form->addElement('course', 'courses', 'Courses', ['multiple' => 1]);
        $this->_form->setDefault('courses', [3,2]);

        $courseslist = $DB->get_records_menu('course', null, 'sortorder', 'id, fullname');
        $this->_form->addElement('select', 'cselect', 'Courses select', $courseslist, ['multiple' => 1, 'size' => 5]);
        $this->_form->setDefault('cselect', [3,2]);

        $this->_form->addElement('tags', 'interests', get_string('interestslist'),
            array('itemtype' => 'user', 'component' => 'core'));

        $this->_form->addElement('course', 'courses1', 'Single course');
        //$this->_form->setDefault('courses1', [2]);

        $this->_form->addElement('advcheckbox', 'enablecselect1', 'Enable cselect1 and text1');
        $this->_form->addElement('select', 'cselect1', 'Courses select (1)', $courseslist);
        $this->_form->disabledIf('cselect1', 'enablecselect1', 'unchecked');

        $this->_form->addElement('text', 'text1', 'Text input', $courseslist);
        $this->_form->disabledIf('text1', 'enablecselect1', 'unchecked');
        $this->_form->setType('text1', PARAM_TEXT);

        $this->add_action_buttons();
    }
}

$form = new testform();
echo $OUTPUT->header();
if ($data = $form->get_data()) {
    print_object($data);
}

$form->display();

echo $OUTPUT->footer();