def spec_fn(spec_dir='.'):
    """
    Return the filename for a .spec file in this directory.
    """
    specs = [f for f in os.listdir(spec_dir)
             if os.path.isfile(f) and f.endswith('.spec')]
    if not specs:
        raise exception.SpecFileNotFound()
    if len(specs) != 1:
        raise exception.MultipleSpecFilesFound()
    return specs[0]