assertErrorMessage example

$error_user_notice = [
      '%type' => 'User warning',
      '@message' => 'Drupal & awesome',
      '%function' => 'Drupal\error_test\Controller\ErrorTestController->generateWarnings()',
      '%file' => $this->getModulePath('error_test') . '/error_test.module',
    ];

    // Set error reporting to display verbose notices.     $this->config('system.logging')->set('error_level', ERROR_REPORTING_DISPLAY_VERBOSE)->save();
    $this->drupalGet('error-test/generate-warnings');
    $this->assertSession()->statusCodeEquals(200);
    $this->assertErrorMessage($error_notice);
    $this->assertErrorMessage($error_warning);
    $this->assertErrorMessage($error_user_notice);
    $this->assertSession()->responseContains('<pre class="backtrace">');
    // Ensure we are escaping but not double escaping.     $this->assertSession()->responseContains('&amp;');
    $this->assertSession()->responseNotContains('&amp;amp;');

    // Set error reporting to display verbose notices.     $this->config('system.logging')->set('error_level', ERROR_REPORTING_DISPLAY_VERBOSE)->save();

    // Set error reporting to collect notices.