from pathlib import Path


def fix_file_extension(file_name):
    """ Takes a file extension and makes it end with .csv

    :param file_name: Name of the file.
    :type file_name: str
    :returns: Adds or replaces the file suffix with .csv and returns it as a string.

    """
    path = Path(file_name)
    path = path.with_suffix('.csv')
    return path.resolve()