class FormValidationMessageOrderTest

class FormValidationMessageOrderTest extends KernelTestBase implements FormInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_validation_error_message_order_test';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        // Prepare fields with weights specified.
        $form['one'] = [
            '#type' => 'textfield',
            '#title' => 'One',
            '#required' => TRUE,
            '#weight' => 40,
        ];
        $form['two'] = [
            '#type' => 'textfield',
            '#title' => 'Two',
            '#required' => TRUE,
            '#weight' => 30,
        ];
        $form['three'] = [
            '#type' => 'textfield',
            '#title' => 'Three',
            '#required' => TRUE,
            '#weight' => 10,
        ];
        $form['four'] = [
            '#type' => 'textfield',
            '#title' => 'Four',
            '#required' => TRUE,
            '#weight' => 20,
        ];
        $form['actions'] = [
            '#type' => 'actions',
            'submit' => [
                '#type' => 'submit',
                '#value' => 'Submit',
            ],
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * Tests that fields validation messages are sorted in the fields order.
     */
    public function testValidationErrorMessagesSortedWithWeight() : void {
        $form_state = new FormState();
        $form_builder = $this->container
            ->get('form_builder');
        $form_builder->submitForm($this, $form_state);
        $messages = \Drupal::messenger()->all();
        \Drupal::messenger()->deleteAll();
        $this->assertTrue(isset($messages['error']));
        $error_messages = $messages['error'];
        $this->assertEquals('Three field is required.', $error_messages[0]);
        $this->assertEquals('Four field is required.', $error_messages[1]);
        $this->assertEquals('Two field is required.', $error_messages[2]);
        $this->assertEquals('One field is required.', $error_messages[3]);
    }

}