Asserting JavaScript alert()'s in Drupal / Mink / Webdriver Tests

You're running Mink / Webdriver tests (or Drupal 8+) Tests and need to assert expected JavaScript errors?

Sounds like an easy task, but doesn't seem very well-supported yet.

After playing around a bit, this pattern is what worked best:

<?php
 public function testExpectedAlert() {
   /**
    * @var \Behat\Mink\Driver\Selenium2Driver $driver
    */
   $driver = $this->getSession()->getDriver();
  // Go to front page and expect the alert to fire:
   try {
     $this->drupalGet('<front>');
   }
   catch (UnexpectedAlertOpen $e) {
     $this->assertTrue(TRUE);
   }
   $message = $driver->getWebDriverSession()->getAlert_text();
   $driver->getWebDriverSession()->accept_alert();
   $this->assertEquals('This is an alert message', $message);
 }
?>

Huge thanks to @Grevil, who found this out with me and wrote these great Drupal Testing Snippets: https://gitlab.com/-/snippets/2264049

Another alternative to test might be

<?php
$this->expectException('UnexpectedAlertOpen');
$this->expectExceptionMessage("Couldn't find page variant to store Panels display");
?>

 Links that might be helpful:

• https://stackoverflow.com/questions/66450025/unexpected-alert-open-causes-error-in-behat-mink-test
• https://stackoverflow.com/questions/19173195/how-to-handle-the-unexpected-alert-open
• https://github.com/php-webdriver/php-webdriver/issues/475
• https://stackoverflow.com/questions/19173195/how-to-handle-the-unexpected-alert-open
• https://git.drupalcode.org/project/varbase/-/commit/f63a9e46255137f19b43889caa1a2cfadc539d3c
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