public function testIds()
    {
        Dropdown::$counter = 0;
        $out = Dropdown::widget(['items' => [['label' => 'Page1', 'content' => 'Page1'], ['label' => 'Dropdown1', 'items' => [['label' => 'Page2', 'content' => 'Page2'], ['label' => 'Page3', 'content' => 'Page3']]], ['label' => 'Dropdown2', 'visible' => false, 'items' => [['label' => 'Page4', 'content' => 'Page4'], ['label' => 'Page5', 'content' => 'Page5']]]]]);
        $expected = <<<EXPECTED
<ul id="w0" class="dropdown-menu"><li class="dropdown-header">Page1</li>
<li class="dropdown-submenu"><a href="#" tabindex="-1">Dropdown1</a><ul class="dropdown-menu"><li class="dropdown-header">Page2</li>
<li class="dropdown-header">Page3</li></ul></li></ul>
EXPECTED;
        $this->assertEqualsWithoutLE($expected, $out);
    }