Issue #3293090 by longwave, pooja saraah, mondrake, alexpott, Gábor Hojtsy:...

namespace Drupal\FunctionalJavascriptTests;

use PHPUnit\Framework\AssertionFailedError;

/**

 * Tests that Drupal.throwError will cause a deprecation warning.

 * Tests that Drupal.throwError will cause a test failure.

 *

 * @group javascript

 * @group legacy

 */

class JavascriptErrorsTest extends WebDriverTestBase {

  protected static $modules = ['js_errors_test'];

  /**

   * Tests that JavaScript console errors will result in a deprecation warning.

   * Tests that JavaScript console errors will result in a test failure.

   */

  public function testJavascriptErrors(): void {

    $this->expectDeprecation('Not failing JavaScript test for JavaScript errors is deprecated in drupal:9.3.0 and is removed from drupal:10.0.0. This test had the following JavaScript errors: Error: A manually thrown error.');

    // Visit page that will throw a JavaScript console error.

    $this->drupalGet('js_errors_test');

    // Ensure that errors from previous page loads will be

    // detected.

    $this->drupalGet('user');

    $this->expectException(AssertionFailedError::class);

    $this->expectExceptionMessageMatches('/^Error: A manually thrown error/');

    // Manually call the method under test, as it cannot be caught by PHPUnit

    // when triggered from assertPostConditions().

    $this->failOnJavaScriptErrors();

  }

  /**

   * Clear the JavaScript error log to prevent this test failing for real.

   *

   * @postCondition

   */

  public function clearErrorLog() {

    $this->getSession()->executeScript("sessionStorage.removeItem('js_testing_log_test.errors')");

  }

}

          @trigger_error('Javascript Deprecation:' . substr($warning, 13), E_USER_DEPRECATED);

        }

      }

    }

    parent::tearDown();

  }

  /**

   * Triggers a test failure if a JavaScript error was encountered.

   *

   * @throws \PHPUnit\Framework\AssertionFailedError

   *

   * @postCondition

   */

  protected function failOnJavaScriptErrors(): void {

    if ($this->failOnJavascriptConsoleErrors) {

      $errors = $this->getSession()->evaluateScript("JSON.parse(sessionStorage.getItem('js_testing_log_test.errors') || JSON.stringify([]))");

      if (!empty($errors)) {

          $all_errors = implode("\n", $errors);

          @trigger_error("Not failing JavaScript test for JavaScript errors is deprecated in drupal:9.3.0 and is removed from drupal:10.0.0. This test had the following JavaScript errors: $all_errors. See https://www.drupal.org/node/3221100", E_USER_DEPRECATED);

        $this->fail(implode("\n", $errors));

      }

    }

    }

    parent::tearDown();

  }

  /**