class SettingsConfigValidationTest

class SettingsConfigValidationTest extends KernelTestBase {
  
  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'image',
  ];
  
  /**
   * Tests that the preview_image setting must be an existing image file.
   */
  public function testPreviewImagePathIsValidated() : void {
    $this->installConfig('image');
    // Drupal does not have a hard dependency on the fileinfo extension and
    // implements an extension-based mimetype guesser. Therefore, we must use
    // an incorrect extension here instead of writing text to a supposed PNG
    // file and depending on a check of the file contents.
    $file = sys_get_temp_dir() . '/fake_image.png.txt';
    file_put_contents($file, 'Not an image!');
    $this->expectException(SchemaIncompleteException::class);
    $this->expectExceptionMessage('[preview_image] This file is not a valid image.');
    $this->config('image.settings')
      ->set('preview_image', $file)
      ->save();
  }

}