trait FilesTestTrait

trait FilesTestTrait {
    
    /**
     * Gets the absolute pathname for a project directory.
     *
     * @param string $directory
     *   The directory to check. If no directory name is passed, it will return
     *   the absolute path for the directory containing the Examples project.
     *
     * @return string
     *   The absolute pathname.
     */
    protected static function projectPathname(string $directory = '') : string {
        // There is no need to use realpath() because __DIR__ is always an absolute
        // path.
        return dirname(__DIR__, 3) . "/{$directory}";
    }
    
    /**
     * Retrieves files in a project directory.
     *
     * @param string $directory
     *   The directory where files are located. It must be an absolute path like
     *   the one returned by
     *   \Drupal\Tests\UnitTestCase\FilesTestTrait::realPath().
     * @param string $extension
     *   The file extension.
     * @param callable $callable
     *   The callable to accept files. It gets the following arguments.
     *     - $current: the current item's value
     *     - $key: the current item's key
     *     - $iterator: the iterator being filtered
     *   It must return TRUE when the file is accepted, FALSE otherwise.
     *
     * @return array
     *   An array
     *
     * @see \RecursiveCallbackFilterIterator
     */
    protected static function retrieveFiles(string $directory, string $extension, callable $callable) : array {
        $directory_iterator = new \RecursiveDirectoryIterator($directory, \FilesystemIterator::SKIP_DOTS);
        $files = [];
        $filter_callback = function (mixed $current, string $key, mixed $iterator) use ($extension, $callable) {
            
            /** @var \SplFileInfo $current */
            
            /** @var \RecursiveDirectoryIterator $iterator */
            if ($current->isFile() && $current->getExtension() === $extension) {
                return call_user_func($callable, $current, $key, $iterator);
            }
            elseif ($current->isDir()) {
                // Always accept a directory.
                return TRUE;
            }
            else {
                return FALSE;
            }
        };
        $filter = new \RecursiveCallbackFilterIterator($directory_iterator, $filter_callback);
        $iterator = new \RecursiveIteratorIterator($filter);
        foreach ($iterator as $info) {
            
            /** @var \SplFileInfo $info */
            $files[] = [
                $info->getFilename(),
                $info->getPath(),
                $info->getPathname(),
            ];
        }
        return $files;
    }

}