class PlaceholderMessageTest

class PlaceholderMessageTest extends BrowserTestBase {
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'render_placeholder_message_test',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    
    /**
     * Tests rendering of message placeholder.
     */
    public function testMessagePlaceholder() {
        $messages_markup = '<div role="contentinfo" aria-label="Status message"';
        $test_routes = [
            // Messages placeholder rendered first.
'render_placeholder_message_test.first',
            // Messages placeholder rendered after one, before another.
'render_placeholder_message_test.middle',
            // Messages placeholder rendered last.
'render_placeholder_message_test.last',
        ];
        $assert = $this->assertSession();
        foreach ($test_routes as $route) {
            // Verify that we start off with zero messages queued.
            $this->drupalGet(Url::fromRoute('render_placeholder_message_test.queued'));
            $assert->responseNotContains($messages_markup);
            // Verify the test case at this route behaves as expected.
            $this->drupalGet(Url::fromRoute($route));
            $assert->elementContains('css', 'p.logged-message:nth-of-type(1)', 'Message: P1');
            $assert->elementContains('css', 'p.logged-message:nth-of-type(2)', 'Message: P2');
            $assert->responseContains($messages_markup);
            $assert->elementExists('css', 'div[aria-label="Status message"] ul');
            $assert->elementContains('css', 'div[aria-label="Status message"] ul li:nth-of-type(1)', 'P1');
            $assert->elementContains('css', 'div[aria-label="Status message"] ul li:nth-of-type(2)', 'P2');
            // Verify that we end with all messages printed, hence again zero queued.
            $this->drupalGet(Url::fromRoute('render_placeholder_message_test.queued'));
            $assert->responseNotContains($messages_markup);
        }
    }

}