/**
 * Determines if a given file in a directory is a directory itself.
 *
 * @param directoryPath - The directory path containing the file.
 * @param fileName - The name of the file.
 * @returns `true` if the file is a directory, `false` otherwise.
 *
 * @example
 * isDirectory('/path/to/directory', 'subdirectory') // returns true
 */
export declare function isDirectory(directoryPath: string, fileName: string): boolean;